I have been challenged to be able to collect any real information on this as it seems to be random, but it has now happened multiple times in the last couple of weeks.
When I am playing music, typically in the car on my phone through Bluetooth which is probably 90%+ of my Plex usage, the volume will suddenly and without warning drop to almost non-audible levels. It sort of reminds me of when a text or other notification comes in and the volume drops, but would come back up, but in this case it never comes back up to normal volume levels. When this occurs I don’t believe I am getting any notification that I am noticing and I should since its audio prompt is typically at full volume while the media volume is reduced so you can hear it. There was one time after it moved on to the next music track that the volume did recover now that I think back, but this is not typical. What I usually have to do is either X the audio player entirely and restart my selection or completely disconnect Bluetooth from my car and re-establish the link and then it is fine. I have checked all my volume sliders in Android and my Bluetooth is still up to maximum when this occurs. If I slide it down the volume goes even lower / can’t hear it at all and if I put it back up to max I can hear it again, but it is too low. For reference if anyone else drives a circa 2010 Mazda I am having to raise my radio volume up to level 43 to hear music normally which should be deafeningly loud.
My memory may be off, but I felt like the Android app made changes recently to make Plex be more pro-active about resuming playback after a call or a notification - which I love btw. I can’t tell you how often I’ll be listening to music with my shower speaker, get a call and then my music would then be stopped until I got out and restarted it so thank you for that. Anyway, this problem seems to have begun after those changes were made and may possibly have something to do with that tweak. I may just be connecting dots that really shouldn’t be, but based on the seeming randomness of the occurrence and therefore my inability to make it happen / investigate more properly I don’t have much of anything more concrete to offer. 
