I didn't encounter any random BT disconnection issue with my 5.2" Zenfone 3, but I do encounter that if battery is below than 50% (I'm sure more than 60% is fine), even when connected to a BT speaker, the speaker wouldn't produce any sound, and this happen when you're charging the phone at the time.

I know, it's really weird. It only gives out sound for a split-second before going silent. I just saw your post and check for update. Yet to install and verify, but I'll update once it's done.

install oreo beta on my phone >< it work great