When I watch the movie from my phone, or watch it on my computer from the plex web app, after maybe 10 minutes, the movie stops playing. I can see that the preload does not continue (the slightly colored section of the timeline does not grow before the playback dot.
I’m local, in case of my computer on gigabit ethernet, so it can’t be bandwidth. In fact, I can copy the whole thing in seconds.
It happens almost every time I watch a series and sometimes 3 times per episode.