tcp.port==443 and ip.addr == 18.104.22.168 and ip.addr == 192.168.1.20
but it is better to add it in tcpdump instead so you can capture also the wan packets.
I didn't forget, just waiting for the issue to re-appear…
Since I won't leave this topic open, the issue hasn't reappeared since I upgraded OpenWRT and reconfigured from scratch.
However, a new issue has appeared on the AP roughly at the same time as I upgraded OpenWRT on the A6.