I made a similar post about the exact same problem here:
Unfortunately after about 3 weeks someone has yet to comment on it or even acknowledge it. This is very disappointing, in both the situation which has gotten worse over the 3 weeks it’s been happening, and in that nothing is or has been done about it to the point of even asking any follow-up questions about the problem or even post a simple acknowledgement that it’s happening.
They are re-packaging or re-transmitting streaming video “channels” from other sources, and it’s possible the problem is coming from wherever the feed originates, but they need to fix it if it’s Plex’s problem, or get it fixed from whoever they get the feed from otherwise. Either way, it used to work fine, then all of a sudden about 3 weeks ago it went to crap, and it’s been that way, perhaps worse, in the 3 weeks or so it’s been happening.
In fact, watching one of the feeds “Comedy Dynamics”, RIGHT NOW JUST CRASHED. Most annoying. Trying to watch anything in the background is impossible because of having to restart the player every half hour or so. This makes the video service almost unusable 
