Fresh builds from your source, the initramfs image boots fine but after sucessfully flashing the sysupgrade image it just reboots to stock firmware.
Here are logs of the process I been using, maybe I'm doing something wrong.
initramfs
(IPQ40xx) # tftpboot openwrt-ipq40xx-generic-netgear_wac510-initramfs-fit-uImage.itb
eth0 PHY0 Down Speed :10 Half duplex
eth0 PHY1 Down Speed :10 Half duplex
eth0 PHY2 Down Speed :10 Half duplex
eth0 PHY3 up Speed :1000 Full duplex
eth0 PHY4 Down Speed :10 Half duplex
Using eth0 device
TFTP from server 192.168.1.15; our IP address is 192.168.1.11
Filename 'openwrt-ipq40xx-generic-netgear_wac510-initramfs-fit-uImage.itb'.
Load address: 0x84000000
Loading: #################################################################
#################################################################
#################################################################
#################################################################
#################################################################
#################################################################
#################################################################
#################################################################
#################################################################
################################################################
done
Bytes transferred = 9515512 (9131f8 hex)
(IPQ40xx) # bootm
## Booting kernel from FIT Image at 84000000 ...
Using 'config@5' configuration
Trying 'kernel@1' kernel subimage
Description: ARM OpenWrt Linux-5.4.79
Type: Kernel Image
Compression: gzip compressed
Data Start: 0x840000e4
Data Size: 9495883 Bytes = 9.1 MiB
Architecture: ARM
OS: Linux
Load Address: 0x80208000
Entry Point: 0x80208000
Hash algo: crc32
Hash value: e7e85939
Hash algo: sha1
Hash value: 976652b80ba0ff16803dbf2686cb91198d15feb2
Verifying Hash Integrity ... crc32+ sha1+ OK
## Flattened Device Tree from FIT Image at 84000000
Using 'config@5' configuration
Trying 'fdt@1' FDT blob subimage
Description: ARM OpenWrt netgear_wac510 device tree blob
Type: Flat Device Tree
Compression: uncompressed
Data Start: 0x8490e768
Data Size: 17757 Bytes = 17.3 KiB
Architecture: ARM
Hash algo: crc32
Hash value: ecfacb31
Hash algo: sha1
Hash value: 6c0fad580a4236c25d242b7577dc201b9031a138
Verifying Hash Integrity ... crc32+ sha1+ OK
Booting using the fdt blob at 0x8490e768
Uncompressing Kernel Image ... OK
Loading Device Tree to 86ff8000, end 86fff55c ... OK
ipq: fdt fixup unable to find compatible node
Using machid 0x8010100 from environment
Starting kernel ...
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 5.4.79 (gingernut@MSI) (gcc version 8.4.0 (OpenWrt GCC 8.4.0 r15037-48d4894357)) #0 SMP Wed Nov 25 13:24:03 2020
[ 0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7), cr=10c5387d
[ 0.000000] CPU: div instructions available: patching division code
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt: Machine model: Netgear WAC510
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] percpu: Embedded 15 pages/cpu s30092 r8192 d23156 u61440
[ 0.000000] Built 1 zonelists, mobility grouping on. Total pages: 64448
[ 0.000000] Kernel command line: root=/dev/ubiblock0_1
[ 0.000000] Dentry cache hash table entries: 32768 (order: 5, 131072 bytes, linear)
[ 0.000000] Inode-cache hash table entries: 16384 (order: 4, 65536 bytes, linear)
[ 0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
[ 0.000000] Memory: 235320K/260096K available (5488K kernel code, 183K rwdata, 1452K rodata, 14336K init, 230K bss, 24776K reserved, 0K cma-reserved, 0K highmem)
[ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
[ 0.000000] rcu: Hierarchical RCU implementation.
[ 0.000000] rcu: RCU calculated value of scheduler-enlistment delay is 10 jiffies.
[ 0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
[ 0.000000] random: get_random_bytes called from start_kernel+0x2f0/0x498 with crng_init=0
[ 0.000000] arch_timer: cp15 timer(s) running at 48.00MHz (virt).
[ 0.000000] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0xb11fd3bfb, max_idle_ns: 440795203732 ns
[ 0.000007] sched_clock: 56 bits at 48MHz, resolution 20ns, wraps every 4398046511096ns
[ 0.000022] Switching to timer-based delay loop, resolution 20ns
[ 0.000244] Calibrating delay loop (skipped), value calculated using timer frequency.. 96.00 BogoMIPS (lpj=480000)
[ 0.000261] pid_max: default: 32768 minimum: 301
[ 0.000461] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
[ 0.000479] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
[ 0.001465] CPU: Testing write buffer coherency: ok
[ 0.002525] Setting up static identity map for 0x80300000 - 0x80300060
[ 0.002664] rcu: Hierarchical SRCU implementation.
[ 0.003112] smp: Bringing up secondary CPUs ...
[ 0.006269] smp: Brought up 1 node, 4 CPUs
[ 0.006288] SMP: Total of 4 processors activated (384.00 BogoMIPS).
[ 0.006297] CPU: All CPU(s) started in SVC mode.
[ 0.011025] VFP support v0.3: implementor 41 architecture 2 part 30 variant 7 rev 5
[ 0.011181] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
[ 0.011207] futex hash table entries: 1024 (order: 4, 65536 bytes, linear)
[ 0.011484] pinctrl core: initialized pinctrl subsystem
[ 0.012571] NET: Registered protocol family 16
[ 0.012865] DMA: preallocated 256 KiB pool for atomic coherent allocations
[ 0.014143] cpuidle: using governor ladder
[ 0.014189] cpuidle: using governor menu
[ 0.034454] cryptd: max_cpu_qlen set to 1000
[ 0.037887] usbcore: registered new interface driver usbfs
[ 0.037952] usbcore: registered new interface driver hub
[ 0.038039] usbcore: registered new device driver usb
[ 0.038086] pps_core: LinuxPPS API ver. 1 registered
[ 0.038095] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[ 0.038121] PTP clock support registered
[ 0.038820] workqueue: max_active 576 requested for napi_workq is out of range, clamping between 1 and 512
[ 0.039914] clocksource: Switched to clocksource arch_sys_counter
[ 0.040795] thermal_sys: Registered thermal governor 'step_wise'
[ 0.041086] NET: Registered protocol family 2
[ 0.041705] tcp_listen_portaddr_hash hash table entries: 512 (order: 0, 6144 bytes, linear)
[ 0.041748] TCP established hash table entries: 2048 (order: 1, 8192 bytes, linear)
[ 0.041785] TCP bind hash table entries: 2048 (order: 2, 16384 bytes, linear)
[ 0.041834] TCP: Hash tables configured (established 2048 bind 2048)
[ 0.041950] UDP hash table entries: 256 (order: 1, 8192 bytes, linear)
[ 0.041991] UDP-Lite hash table entries: 256 (order: 1, 8192 bytes, linear)
[ 0.042225] NET: Registered protocol family 1
[ 0.042265] PCI: CLS 0 bytes, default 64
[ 0.259588] workingset: timestamp_bits=14 max_order=16 bucket_order=2
[ 0.265252] squashfs: version 4.0 (2009/01/31) Phillip Lougher
[ 0.265267] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
[ 0.316510] bam-dma-engine 8e04000.dma: num-channels unspecified in dt
[ 0.316531] bam-dma-engine 8e04000.dma: num-ees unspecified in dt
[ 0.317803] tcsr 1949000.tcsr: setting wifi_glb_cfg = 41000000
[ 0.317893] tcsr 194b000.tcsr: setting usb hs phy mode select = e700e7
[ 0.317978] tcsr 1953000.ess_tcsr: setting ess interface select = 0
[ 0.318060] tcsr 1957000.tcsr: setting wifi_noc_memtype_m0_m2 = 2222222
[ 0.318390] Serial: 8250/16550 driver, 2 ports, IRQ sharing disabled
[ 0.318972] msm_serial 78af000.serial: msm_serial: detected port #0
[ 0.319016] msm_serial 78af000.serial: uartclk = 1843200
[ 0.319069] 78af000.serial: ttyMSM0 at MMIO 0x78af000 (irq = 25, base_baud = 115200) is a MSM
[ 0.319095] msm_serial: console setup on port #0
[ 0.798201] printk: console [ttyMSM0] enabled
[ 0.803126] msm_serial: driver initialized
[ 0.812319] loop: module loaded
[ 0.814487] spi_qup 78b5000.spi: IN:block:16, fifo:64, OUT:block:16, fifo:64
[ 0.821447] random: fast init done
[ 0.824238] spi-nor spi0.0: s25fl016k (2048 Kbytes)
[ 0.824824] 9 fixed-partitions partitions found on MTD device spi0.0
[ 0.829547] Creating 9 MTD partitions on "spi0.0":
[ 0.836181] 0x000000000000-0x000000040000 : "0:SBL1"
[ 0.841704] 0x000000040000-0x000000060000 : "0:MIBIB"
[ 0.846660] 0x000000060000-0x0000000c0000 : "0:QSEE"
[ 0.851674] 0x0000000c0000-0x0000000d0000 : "0:CDT"
[ 0.856651] 0x0000000d0000-0x0000000e0000 : "0:DDRPARAMS"
[ 0.861346] 0x0000000e0000-0x0000000f0000 : "0:APPSBLENV"
[ 0.866812] 0x0000000f0000-0x0000001e0000 : "0:APPSBL"
[ 0.872252] 0x0000001e0000-0x0000001f0000 : "0:MANUDATA"
[ 0.877223] 0x0000001f0000-0x000000200000 : "0:ART"
[ 0.883499] spi-nand spi0.1: Winbond SPI NAND was found.
[ 0.886499] spi-nand spi0.1: 128 MiB, block size: 128 KiB, page size: 2048, OOB size: 64
[ 0.892454] 4 fixed-partitions partitions found on MTD device spi0.1
[ 0.900153] Creating 4 MTD partitions on "spi0.1":
[ 0.906470] 0x000000000000-0x000003800000 : "rootfs"
[ 1.084181] mtd: device 9 (rootfs) set to be root filesystem
[ 1.085135] mtdsplit: no squashfs found in "rootfs"
[ 1.088932] 0x000003800000-0x000007000000 : "rootfs_1"
[ 1.266502] 0x000007000000-0x000007f00000 : "var_config"
[ 1.313599] 0x000007f00000-0x000007fc0000 : "Oops_log"
[ 1.319791] libphy: ipq40xx_mdio: probed
[ 1.413573] ESS reset ok!
[ 1.446618] ESS reset ok!
[ 1.864823] libphy: Fixed MDIO Bus: probed
[ 1.869247] i2c /dev entries driver
[ 1.871350] sdhci: Secure Digital Host Controller Interface driver
[ 1.871544] sdhci: Copyright(c) Pierre Ossman
[ 1.877790] sdhci-pltfm: SDHCI platform and OF driver helper
[ 1.885768] NET: Registered protocol family 10
[ 1.889323] Segment Routing with IPv6
[ 1.892335] NET: Registered protocol family 17
[ 1.895984] 8021q: 802.1Q VLAN Support v1.8
[ 1.900376] Registering SWP/SWPB emulation handler
[ 1.91390▒[ 1.934838] Freeing unused kernel memory: 14336K
[ 1.992863] Run /init as init process
[ 2.021305] init: Console is alive
[ 2.021545] init: - watchdog -
[ 2.037300] kmodloader: loading kernel modules from /etc/modules-boot.d/*
[ 2.043054] dwc3-qcom 8af8800.usb3: IRQ hs_phy_irq not found
[ 2.043100] dwc3-qcom 8af8800.usb3: IRQ dp_hs_phy_irq not found
[ 2.048816] dwc3-qcom 8af8800.usb3: IRQ dm_hs_phy_irq not found
[ 2.054515] dwc3-qcom 8af8800.usb3: IRQ ss_phy_irq not found
[ 2.062141] dwc3-qcom 60f8800.usb2: IRQ hs_phy_irq not found
[ 2.066263] dwc3-qcom 60f8800.usb2: IRQ dp_hs_phy_irq not found
[ 2.071934] dwc3-qcom 60f8800.usb2: IRQ dm_hs_phy_irq not found
[ 2.077544] dwc3-qcom 60f8800.usb2: IRQ ss_phy_irq not found
[ 2.085817] dwc3 8a00000.dwc3: Failed to get clk 'ref': -2
[ 2.214822] dwc3 6000000.dwc3: Failed to get clk 'ref': -2
[ 2.319155] xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
[ 2.319238] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 1
[ 2.323896] xhci-hcd xhci-hcd.0.auto: hcc params 0x0228f665 hci version 0x100 quirks 0x0000000002010010
[ 2.331271] xhci-hcd xhci-hcd.0.auto: irq 94, io mem 0x08a00000
[ 2.343057] hub 1-0:1.0: USB hub found
[ 2.346425] hub 1-0:1.0: 1 port detected
[ 2.350576] xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
[ 2.354295] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 2
[ 2.359582] xhci-hcd xhci-hcd.0.auto: Host supports USB 3.0 SuperSpeed
[ 2.367267] usb usb2: We don't know the algorithms for LPM for this host, disabling LPM.
[ 2.374329] hub 2-0:1.0: USB hub found
[ 2.382120] hub 2-0:1.0: 1 port detected
[ 2.386017] xhci-hcd xhci-hcd.1.auto: xHCI Host Controller
[ 2.389626] xhci-hcd xhci-hcd.1.auto: new USB bus registered, assigned bus number 3
[ 2.395157] xhci-hcd xhci-hcd.1.auto: hcc params 0x0220f665 hci version 0x100 quirks 0x0000000002010010
[ 2.402554] xhci-hcd xhci-hcd.1.auto: irq 95, io mem 0x06000000
[ 2.412718] hub 3-0:1.0: USB hub found
[ 2.417776] hub 3-0:1.0: 1 port detected
[ 2.421897] xhci-hcd xhci-hcd.1.auto: xHCI Host Controller
[ 2.425651] xhci-hcd xhci-hcd.1.auto: new USB bus registered, assigned bus number 4
[ 2.430971] xhci-hcd xhci-hcd.1.auto: Host supports USB 3.0 SuperSpeed
[ 2.438600] usb usb4: We don't know the algorithms for LPM for this host, disabling LPM.
[ 2.445656] hub 4-0:1.0: USB hub found
[ 2.453390] hub 4-0:1.0: config failed, hub doesn't have any ports! (err -19)
[ 2.459581] kmodloader: done loading kernel modules from /etc/modules-boot.d/*
[ 2.465128] init: - preinit -
[ 2.719319] random: jshn: uninitialized urandom read (4 bytes read)
[ 2.770266] random: jshn: uninitialized urandom read (4 bytes read)
[ 2.797669] random: jshn: uninitialized urandom read (4 bytes read)
[ 2.940011] ess_edma c080000.edma: eth0: GMAC Link is down
Press the [f] key and hit [enter] to enter failsafe mode
Press the [1], [2], [3] or [4] key and hit [enter] to select the debug level
[ 6.091570] ess_edma c080000.edma: eth0: GMAC Link is up with phy_speed=1000
[ 6.092487] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 7.185876] ess_edma c080000.edma: eth0: GMAC Link is down
[ 7.193268] procd: - early -
[ 7.193413] procd: - watchdog -
[ 7.737587] procd: - watchdog -
[ 7.741209] procd: - ubus -
[ 7.765995] urandom_read: 5 callbacks suppressed
[ 7.766006] random: ubusd: uninitialized urandom read (4 bytes read)
[ 7.793793] random: ubusd: uninitialized urandom read (4 bytes read)
[ 7.796834] procd: - init -
Please press Enter to activate this console.
[ 8.132916] kmodloader: loading kernel modules from /etc/modules.d/*
[ 8.145865] urngd: v1.0.2 started.
[ 8.161783] Mirror/redirect action on
[ 8.167881] u32 classifier
[ 8.167905] input device check on
[ 8.169475] Actions configured
[ 8.181901] Loading modules backported from Linux version v5.8-0-gbcf876870b95
[ 8.181937] Backport generated by backports.git v5.8-1-0-g79400d9e
[ 8.210863] xt_time: kernel timezone is -0000
[ 8.212803] random: crng init done
[ 8.250012] PPP generic driver version 2.4.2
[ 8.251106] NET: Registered protocol family 24
[ 8.290063] ath10k_mac_create, priv_size: 924 hw: 773f9313 hw->priv: c7ccfdc2
[ 8.948334] ath10k_ahb a000000.wifi: qca4019 hw1.0 target 0x01000000 chip_id 0x003b00ff sub 0000:0000
[ 8.948384] ath10k_ahb a000000.wifi: kconfig debug 0 debugfs 1 tracing 0 dfs 1 testmode 0
[ 8.961327] ath10k_ahb a000000.wifi: firmware ver 10.4b-ct-4019-fW-13-8c5b2baa2 api 5 features mfp,peer-flow-ctrl,txstatus-noack,wmi-10.x-CT,ratemask-CT,regdump-CT,txrate-CT,flush-all-CT,pingpong-CT,ch-regs-CT,nop-CT,set-special-CT,tx-rc-CT,cust-stats-CT,txrate2-CT,beacon-cb-CT,wmi-block-ack-CT,wmi-bcn-rc-CT crc32 1f3ed50f
[ 9.012368] ath10k_ahb a000000.wifi: board_file api 2 bmi_id 0:16 crc32 b5a85a38
[ 10.320017] ath10k_ahb a000000.wifi: unsupported HTC service id: 1536
[ 10.321448] ath10k_ahb a000000.wifi: 10.4 wmi init: vdevs: 16 peers: 48 tid: 96
[ 10.325449] ath10k_ahb a000000.wifi: msdu-desc: 2500 skid: 32
[ 10.373860] ath10k_ahb a000000.wifi: wmi print 'P 48/48 V 16 K 144 PH 176 T 186 msdu-desc: 2500 sw-crypt: 0 ct-sta: 0'
[ 10.374864] ath10k_ahb a000000.wifi: wmi print 'free: 53252 iram: 13576 sram: 35752'
[ 10.514460] ath10k_ahb a000000.wifi: htt-ver 2.2 wmi-op 6 htt-op 4 cal pre-cal-file max-sta 32 raw 0 hwcrypto 1
[ 10.673850] ath10k_mac_create, priv_size: 924 hw: aa79fa0e hw->priv: 3c74fbdd
[ 11.434466] ath10k_ahb a800000.wifi: qca4019 hw1.0 target 0x01000000 chip_id 0x003b00ff sub 0000:0000
[ 11.434512] ath10k_ahb a800000.wifi: kconfig debug 0 debugfs 1 tracing 0 dfs 1 testmode 0
[ 11.453707] ath10k_ahb a800000.wifi: firmware ver 10.4b-ct-4019-fW-13-8c5b2baa2 api 5 features mfp,peer-flow-ctrl,txstatus-noack,wmi-10.x-CT,ratemask-CT,regdump-CT,txrate-CT,flush-all-CT,pingpong-CT,ch-regs-CT,nop-CT,set-special-CT,tx-rc-CT,cust-stats-CT,txrate2-CT,beacon-cb-CT,wmi-block-ack-CT,wmi-bcn-rc-CT crc32 1f3ed50f
[ 11.500223] ath10k_ahb a800000.wifi: board_file api 2 bmi_id 0:17 crc32 b5a85a38
[ 12.807345] ath10k_ahb a800000.wifi: unsupported HTC service id: 1536
[ 12.808213] ath10k_ahb a800000.wifi: 10.4 wmi init: vdevs: 16 peers: 48 tid: 96
[ 12.812841] ath10k_ahb a800000.wifi: msdu-desc: 2500 skid: 32
[ 12.849476] ath10k_ahb a800000.wifi: wmi print 'P 48/48 V 16 K 144 PH 176 T 186 msdu-desc: 2500 sw-crypt: 0 ct-sta: 0'
[ 12.851219] ath10k_ahb a800000.wifi: wmi print 'free: 53252 iram: 13576 sram: 35752'
[ 12.972955] ath10k_ahb a800000.wifi: htt-ver 2.2 wmi-op 6 htt-op 4 cal pre-cal-file max-sta 32 raw 0 hwcrypto 1
[ 13.128524] kmodloader: done loading kernel modules from /etc/modules.d/*
[ 23.894810] ess_edma c080000.edma: eth0: GMAC Link is up with phy_speed=1000
[ 23.896060] br-lan: port 1(eth0) entered blocking state
[ 23.901008] br-lan: port 1(eth0) entered disabled state
[ 23.906251] device eth0 entered promiscuous mode
[ 23.926764] ess_edma c080000.edma: eth1: GMAC Link is down
[ 24.971216] br-lan: port 1(eth0) entered blocking state
[ 24.971257] br-lan: port 1(eth0) entered forwarding state
[ 24.976030] IPv6: ADDRCONF(NETDEV_CHANGE): br-lan: link becomes ready