I have had a issue occuring randomly for some time. I select an TV episode or movie(less common) and it plays for 1-5 seconds, then the video ends and Plex recommends I play the next episode or restart the current one. Generally if I restart the episode it plays fine but not always.
It's not all the time but I was able to reproduce it one night and there was no huge CPU or memory spikes. I also validated that the video was being direct played (no transcoding required).
I have had this happen on my Nexus 5x, Amazon fire 7 tablet and Android tv. This leads me to believe the problem is server side, but all the clients are over WiFi (the tv was hard wired and still had this problem, it is on wifi now though). PMS is installed on a 2nd or 3rd gen core i3 running Windows 10 off a SSD with plenty of free memory