Following this. Mine is doing the exact same thing.
Yes, I have a series 8 75" and my JBL 9.1 sound bar is doing the same thing.
I have been told by TCL that they will provide me with a replacement TV. We'll see if they actually come through. I've been hounding them since the beginning of November. This is definitely not an isolated issue, but doesn't seem widespread enough to hit TCL's/Roku's radar.
Same issues just emailed support let's see what happens