I’ve had this happen a couple times now, on two different TVs with built-in Chromecast. Out of nowhere the app will cast itself to the TV and take over the screen but nothing will play, it is just the app logo. I had previously cast and listened to music earlier in the day but disconnected and cast other media/apps since. A couple of the times it will take over the screen when I am in the middle of watcing something.
It also will reconnect even after the app has been closed out again after this happening already. I actually had it turn on the TV in the middle of the night one time. I’m not sure the length of time after closing the app that it happens, may be random with no set timeframe.
Android App version 11.1.0 on an Android 11 tablet