I am experiencing the exact same thing with auto upgrade, didn't try to install manually or even via a button though - hope it will resolve by itself. Based on the uptime it reboots but still stays on the same firmware. Logs contain same fragments you posted multiple times - looks like there are...
I experienced the same annoying issue with call drops for 10-15 seconds and disabling NAT acceleration finally enabled smooth roaming for me without call drops:
Hello @HBTA, I experienced the same issue with 10-20 seconds delay after switching between AiMesh nodes (RT-AC68U + RP-AC55). The interesting part is that ping monitoring utilities (on both iOS, Android and just ping on Windows) worked perfectly during the node switch, at most one packet 100ms...