Thank you for your feedback. Please try force stopping the app, clearing its cache and rebooting the device to see if the problem persists. If it does, please send us an error report to help us debug the issue. We apologize for the inconvenience and appreciate your contribution to the beta program.
One UI Beta Team
To "fix" this, just open Samsung Music, click on the 3 dots, click on Settings, scroll to the bottom and undo the toggle for "Allow external devices to start playback".