I only use Plex for music.
The Android app only plays a few seconds of music before it stops, then it’ll start again after a few seconds, then stop again. It didn’t used to do this, but in case the bandwidth was an issue I change the quality from original to 96kbps, no difference - no change.
On the same device I then tried the web client - that works fine.
This only happens when the phone is on GPRS, on WiFi it always seems to be fine.
Tom