RT-AC86U firmware upgraded from 384.11_2 to 384.12 with no issues. First shot over WiFi.
This router was never reset for >12 months and the firmware was upgraded multiple times with no issues. Running on Asuswrt-Merlin since day one. I don't know why some people always recommend reset/nuke/bleach/sandblast

routers all the time. Based on my experience, reset and manual setup is needed only when the router wasn't configured properly the first time and the configuration errors are carried over to the new firmware updates.