If the notification player shows up while playing but disappears after the playback is paused for some time, it is possible that Castbox is killed by the system in the background.

Please go to your phone Settings - Apps - Castbox - Battery - Optimize battery usage to check if Castbox battery usage has been "optimized", if it is optimized, please turn off this battery optimize feature for Castbox so the app will not be restricted running in the background.