Casting from iOS stops after about 1 minute

I also get this, after 30 seconds it stops casting.

If I start to play something and immediately lock my phone when it starts playing, it stops after exactly 30 seconds.

If I keep plex open on my phone for 30 seconds and then lock my phone it continues to play.

Not my chromecast because I can cast with other apps without the problem.

EXTREMELY FRUSTRATING!!!