Under the Beam’s room settings, increase the Group Audio Delay setting.

Given that the density of an TV audio stream from a Beam is greater than a normal music stream, it’s possible you’re suffering from enough wifi interference to bother one, but not the other.

I’d also, if the data in that FAQ doesn’t help, recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

It is happened by having the delay too fast so your router don't have enough power/time to pass the information (audio) to tour Move 2, try to connect your Beam with Ethernet cable if you need the minor delay :)

Note, however, for TV input to the Beam, there will always be a slight delay between the Beam’s room, and any ‘grouped’ room. This is due to the nature of the way Sonos buffers data. While streaming music, you won’t see it, but while playing the TV input, you will. But that doesn’t mean there should be dropouts, like you’ve been experiencing. Delay is absolutely not dropouts.