Try connecting the Beam directly to the router with an ethernet cable.

Not sure that would make a difference… the Beam is directly connected to the TV, and it’s wifi capabilities are moot at that point, unless the dropping was on the grouped rooms.

Is the Beam connected to the TV via ARC (HDMI cable) or via optical (connected from TV to adapter on Beam)? 

I’d be looking pretty strongly in either case at the TV set, which seems to be “losing” its connection/knowledge where the speaker is. In leaning towards an ARC connection, which is more common, it could be a loose HDMI cable, either to the TV, or the Beam, potentially, or it could be as easy as updating the firmware on the TV set from the manufacturer. And it of course never hurts to power cycle a Sonos device, it could also be an issue resolved by reloading the software. But any Sonos component is “relatively” dumb when connected to the TV. The Sonos gets “smart” once it receives the data, but the TV doesn’t have access to any of that. Pretty much all the Sonos is doing is sending a signal to the TV that it’s a speaker, and can handle X codecs. It’s up to the firmware in the TV to recognize that there is a speaker connected, and to send it the appropriate data. 

I’d start there, at least.