Hi, I have exactly the same issue!
I also seem to have lip sync issue since I changed the TV - I had the Sonos Arc connected via the regular ARC port on my previous Samsung with no noticable issues? It only seems to do it on the HD channels which seems odd?
It seems on research and from posts on the Sonos forums that any Samsung TV with a one connect box is having issues with eARC. Hopefully Samsung can investigate further.
Feedback from Sonos
Shamsung are aware if this issue it effects the 2018/2019 Qled models as the tv can not decode the dolby algorithm. You will need to purchase a separate av reciever to decode dolby. Samsung will not amit or fix this fault. My complaint was escalated to Samsung HQ and their dinal response "that the issue being reported would be due to a Dolby processing algorithm that cannot be adjusted any further through Samsung."
If you need to complain the highest point of contact to email is ******* it'll save you hours ob the phone and if they recieve enough complaints maybe they will fix this ongoing issue.