D7800 cannot start 802.11nac

I'm using the OpenWrt 19.07.3 stock firmware.

[ 4383.398691] ath10k_pci 0000:01:00.0: peer-unmap-event: unknown peer id 0
[ 4395.235962] ath10k_pci 0000:01:00.0: 10.4 wmi init: vdevs: 16  peers: 48  tid: 96
[ 4395.235998] ath10k_pci 0000:01:00.0: msdu-desc: 2500  skid: 32
[ 4395.311881] ath10k_pci 0000:01:00.0: wmi print 'P 48/48 V 16 K 144 PH 176 T 186  msdu-desc: 2500  sw-crypt: 0 ct-sta: 0'
[ 4395.312672] ath10k_pci 0000:01:00.0: wmi print 'free: 34244 iram: 32964 sram: 6508'
[ 4395.647420] ath10k_pci 0000:01:00.0: Firmware lacks feature flag indicating a retry limit of > 2 is OK, requested limit: 4
[ 4395.647696] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 4395.659932] ath10k_pci 0000:01:00.0: peer-unmap-event: unknown peer id 0

This log doesn't show anything. Don't cut the log short to show what you think you want to show.
You should also provide wifi config.

That's all I could find in dmesg since it got repeated every time I try to bring that interface up.

Anyway, rebooting apparently solved the problem at least for now.

Is a normal message that will always happen, it doesn't say anything about IPv6 being functional or not (it just needlessly says that IPv6 wasn't available at that point in time, which is normal, as it needs a little more time to establish - the kernel tried and complained a bit too early).