I finally got my FP3 last Monday - after having the delivery delayed, so the “audio issue” could be fixed. Using only BT headphones and the speaker, the whole week went flawless audiowise - but unfortunately the speakers have started to inexplicably mute from time to time now. When and why seems quite mysterious. E.g. on Instagram an Instastory video might play with sound while durig the same session a video on my Instagram timeline is muted (even though I visibly turned up the volume) or vice versa.
It seems I can revive the sound by switching to my music app (PowerAmp) and then start and stop and start a song again.
I have no idea why this behaviour started after four flawless days and certainly hope it can be fixed with an update - as at least this “audio issue” seems to not have been fixed by revising the latest batch of the phones.