I can only say my Arc Ultra does not do this with my 2019 Samsung. If it happens again make a diagnostic in the Sonos app within 15 minutes of it happening and call Sonos.
Try this…
Leave the Arc connected and disconnect one of the other devices one at a time to see if the behavior continues. My point being that maybe your TV can’t handle that many devices at one time.
If the above trouble shooting shows no sign of change then it may have to do with the TV trying to negotiate CEC with the Arc and rebooting each time to make the handshake.
Also, if you follow @106rallye advice be sure not to factory reset the Arc. Doing so will erase any data that might be captured in a diagnostic that may be helpful to Sonos Tech Support.
EDIT: I researched your Sony Model era 2016. I see saw it has Bravia Sync which is Sony’s proprietary version of CEC. There is no standard code; so CEC implementation varies by manufacturer. Sony’s Bravia Sync is most likely where the issue lies.
I do own a Sony Bravia Model KDL-46HX800 circa 2010. Much older than your 2016. I have a Beam2 with Era 100’s and Sub-Mini connected via HDMI ARC along with AppleTV 4K and Comcast cable box using the Comcast remote. I’m not experiencing any of the issues you are.
I might contact Sony Tech Support to see what they have to say regarding the Bravia Sync (as it was designed in 2016) when using a 3rd party soundbar. You might also see if there is a firmware/software update available which can usually be found in the “About Menu”.
@AjTrek1, thanks for the advice. I tried disconnecting the other devices but it did not help. It does look like Bravia Sync is the culprit. I will try contacting Sony and look for any software update.