After I applied the :
disassoc_low_ack=0
max_inactivity=900
skip_inactivity_poll=1
The "no connecitity" issue has not occurred again but not enough days have passed.
Could you try to apply those also to both wifi interfaces to see if you get disconnected ?
I applied them the via uci:
uci set wireless.wifinet0.disassoc_low_ack='0'
uci set wireless.wifinet1.disassoc_low_ack='0'
uci set wireless.wifinet0.max_inactivity='900'
uci set wireless.wifinet1.max_inactivity='900'
uci set wireless.wifinet0.skip_inactivity_poll='1'
uci set wireless.wifinet1.skip_inactivity_poll='1'
uci commit wireless
wifi