Kernel errors occur from time to time (modded TL-WR941ND V3)

Hi everyone.
Occasionally (in mean one time per day) occurs kernel errors similar kind:

[33096.426366] ------------[ cut here ]------------
[33096.431045] WARNING: CPU: 0 PID: 0 at backports-4.19.112-1/net/mac80211/rx.c:4527 0x82f2598c [mac80211@82f00000+0x61de0]
[33096.441910] Rate marked as an HT rate but passed status->rate_idx is not an MCS index [0-76]: 78 (0x4e)
[33096.451274] Modules linked in: ath9k ath9k_common ath9k_hw ath nf_conntrack_netlink mac80211 iptable_nat iptable_mangle iptable_filter ipt_REJECT ipt_MASQUERADE ip_tables cfg80211 xt_time xt_tcpudp xt_state xt_nat xt_multiport xt_mark xt_mac xt_limit xt_conntrack xt_comment xt_TCPMSS xt_REDIRECT xt_LOG xt_FLOWOFFLOAD x_tables wireguard nfnetlink nf_reject_ipv4 nf_nat_redirect nf_nat_masquerade_ipv4 nf_conntrack_ipv4 nf_nat_ipv4 nf_nat nf_log_ipv4 nf_log_common nf_flow_table_hw nf_flow_table nf_defrag_ipv4 nf_conntrack_rtcache nf_conntrack compat udp_tunnel tun usb_storage ehci_platform sd_mod scsi_mod ehci_hcd gpio_button_hotplug ext4 mbcache jbd2 usbcore nls_base usb_common crc16 crc32c_generic crypto_hash
[33096.513902] CPU: 0 PID: 0 Comm: swapper Not tainted 4.14.172 #0
[33096.519805] Stack : 80433640 803823c4 00000000 00000000 00000000 00000000 00000000 00000000
[33096.528169]         00000000 00000000 00000000 00000000 00000000 00000001 83807ce0 301d5901
[33096.536519]         83807d78 00000000 00000000 00000000 00000038 8035b7d8 2e31342e 31373220
[33096.544894]         65726963 00000010 ffffff80 20637279 00000000 00000000 82f2598c 82f5ce60
[33096.553259]         00000009 000011af 00000000 82d7fc18 00000002 80226538 00000000 80430000
[33096.561622]         ...
[33096.564064] Call Trace:
[33096.564086] [<8035b7d8>] 0x8035b7d8
[33096.570019] [<82f2598c>] 0x82f2598c [mac80211@82f00000+0x61de0]
[33096.575939] [<80226538>] 0x80226538
[33096.579435] [<8006bd2c>] 0x8006bd2c
[33096.582916] [<8006bd34>] 0x8006bd34
[33096.586397] [<8008298c>] 0x8008298c
[33096.589904] [<82f2598c>] 0x82f2598c [mac80211@82f00000+0x61de0]
[33096.595836] [<800829c4>] 0x800829c4
[33096.599345] [<82f2598c>] 0x82f2598c [mac80211@82f00000+0x61de0]
[33096.605252] [<80285190>] 0x80285190
[33096.608770] [<8011df8c>] 0x8011df8c
[33096.612305] [<82ee701c>] 0x82ee701c [ath9k@82ee0000+0x158d0]
[33096.617973] [<82ef0000>] 0x82ef0000 [ath9k@82ee0000+0x158d0]
[33096.623640] [<82ee6ffc>] 0x82ee6ffc [ath9k@82ee0000+0x158d0]
[33096.629286] [<80085600>] 0x80085600
[33096.632795] [<82ee47c0>] 0x82ee47c0 [ath9k@82ee0000+0x158d0]
[33096.638464] [<80085884>] 0x80085884
[33096.641943] [<800aeb4c>] 0x800aeb4c
[33096.645427] [<8035f7f8>] 0x8035f7f8
[33096.648921] [<800b2644>] 0x800b2644
[33096.652400] [<80360000>] 0x80360000
[33096.655884] [<801efc98>] 0x801efc98
[33096.659379] [<80066e98>] 0x80066e98
[33096.664345] ---[ end trace 00a6c2a65adb4770 ]---

Ordinary functionality works fine, this errors don't interfere with his normal work.
But I want figure out, why these errors appears and try to fix these.

Looks like it is archived by still not fixed bug #6411. If this bug is archived, where can I create this bug?

Just a warning, do not test a master snapshot on this hardware.

Currently running version is:

OpenWrt 19.07-SNAPSHOT, r10997-5b9b833f8c
root@OpenWrt:~# uname -a
Linux OpenWrt 4.14.172 #0 Tue Apr 7 13:51:11 2020 mips GNU/Linux

As I understand from link your provided I can patch some source files and this errors will no more appears?

That's not what I said, nor what the link implied. Under normal circumstances I would have suggested to test a more current master snapshot, but in this case kernel 4.19 would brick this device (v2 and v3 are identical) - and this device is hard to recover (serial console and bridging SMD pads required), so I'm merely warning against testing this.

Given that this device is on its last leg (4/32), I would suggest looking into a suitable replacement soon.

I've understanded, thanks.
I've already done RAM and flash modification to this device: now I have 64 MB RAM and 16 MB flash.
For now I will not try to overcome this errors (because they really don't interfere), but it's one more reason for me to update hardware...