Plexamp has always seemed to have issues with staying open in the background while casting, but it’s gotten worse recently. I can see my phone constantly closing it out and opening it back up by looking at my lockscreen and seeing the currently playing song disappear and reappear multiple times a minute. I tried whitelisting the app from the phones built in battery saver features, but no luck.
Your logs indicate the player service is being destroyed and recreated over and over again. There’s no indication of why it’s being destroyed, which usually means the OS is killing it because it doesn’t think it’s active.
Well, that sucks. I’m on Plexamp version 3.4.1 - according to my phone it’s the latest version available from the play store. It’s on a Pixel 5 running completely stock software, so no weird memory/battery saving apps to speak of…next time I cast I’ll pull another log and see if I spot that same line.