Found what appears to be a bug in Plexamp 3.1.1 - basically trying to pair a bluetooth speaker which succeeds but then the speaker disconnects and reconnects again. It tries this twice, at other times it turns off/crashes. It appears its only if Plexamp is open and a FLAC file is playing at the time.
If I close Plexamp and open Music app or Plexamp and play an MP3 it seems to be fine.
I realise this is a pretty poor bug report but hoping someone will read this who has also experienced this. The speaker is a Jawbone Jambox Big.