I understand that there are some ongoing issues with some models of Samsung TV’s and soundbars from various manufacturers.
It’s been mentioned here in the community that a temporary workaround in some cases, is to switch off eARC on the Samsung TV and just use HDMI-ARC with AnyNet+ enabled and use DD+ (Atmos) audio, rather than LPCM multi-channel audio, and see if that works, until such time as either Samsung (or maybe Sonos) fix the issue. If that doesn’t fix it, then try disabling the CEC protocol on ‘other’ devices connected to the TV’s HDMI ports, but then powercycle those devices and the TV (and the Beam too).
Hope that assists.