In my case, one network band disappeared completely and there were seldom some problems (eg, kicking out from user session when accessing System Logs page on router web portal, also some other problems now don't remember what it was...). This time I did reboot a few times, but didn't tried to...
This happened also to my RT-AC86U. I have this model only for couple of months. Was using Merlin firmware from the first day (mainly due to the temperature sensor readings in admin portal - I aslo installed heat dissipation fans). During past weeks it was behaving unstable - WiFi sometimes was...