Did you make a diagnostic after this happened and called Sonos? Do not reset before you’ve done that.

Rather than a Factory Reset, will a reboot (remove power for 30 or more seconds) recover the unit?

Regardless, your unit’s behavior is not normal. There will be data in the diagnostic that will help identify the issue. Unfortunately, this is a long weekend and support will be closed. You could post a diagnostic confirmation number here. Maybe a staff member will drop by and check your diagnostic.

I suggest that you also submit a diagnostic while the unit is operating.

Are there any error messages?

Also, can you please answer the following questions:

1/ What is the source of the programme? 

2/ Does this happen from any other source?

3/ How is the Beam connected to the source?

4/ The next time this happens, can you open the Sonos App and select the Beam using the middle button at the bottom of the App and check that TV source is still shown?