I would first see what happens when you disconnect the ‘other’ devices from your TV HDMI ports and just leave the Arc connected and see if something connected to the TV is causing the issue by stealing the CEC focus. If the TV permits, also try switching the Sonos Arc HDMI port between eARC and Arc and see if that changes anything.

If the issue persists after trying the above, then when you next encounter the issue, It maybe best to submit a Sonos system diagnostic report from within the Sonos App and either note/post it’s reference back here and then contact/chat with Sonos Support Staff via this LINK  and see what the Staff can suggest to resolve the matter.