There's an old thread that touched upon this but seems to have been forgotten.

The issue is 2-3 years old.

Steps to reproduce:

1. Make a queue/playlist

2. Start playing

3. Cast to a Chromecast-enabled device

4. Wait for playback to finish

5. After the music stops, the homescreen widget is nowhere to be found

Tested with a Samsung Galaxy S23 Ultra and a Google Nest Audio speaker