I am on OpenWrt SNAPSHOT r18777-1847382456 i have not stumbled yet on that issue yet, the wlan0 went completely down if I get it correctly ...
I got also a phew "unknown event 139" but wifi did not not went down.
Which snapshot are you using ?
Forum user @ex-git suggested at [Belkin RT3200/Linksys E8450 WiFi AX discussion] for another issue I don't know if it is related.
(Belkin RT3200/Linksys E8450 WiFi AX discussion - #1719 by ex-git)
echo 0 > /sys/kernel/debug/ieee80211/phy0/aql_enable
echo 0 > /sys/kernel/debug/ieee80211/phy1/aql_enable