I have seen several posts of BEAM using HDMI ARC (in my case with a Samsung TV).
Sound works for little bit and then cuts off.
Fixes I usually see are unplug TV and Sonos and replug and try again. That does not fix it for me. I did see something about and update...but my BEAM is updated. I love Sonos...but this is killing me. I wonder if I am still within my return period.