Just wanted to add my 65” 615 started having this issue a couple days ago. As suggested I did the restart but that only helps until you change inputs. I did the setting reset and I believe it was an input change that made the issue return. Finally did a full factory reset and which it’s only been a day the issue has not returned with input change, on/off, or anything.
Yeah, it seems to just be happening on the 6 series. They either need to roll out a new update, which would be easy you'd think, or replace everybody's TV, that voices that they have this issue, that is under warranty. Which would be very pricey. But they need to fix it quick. If not I'll never buy TCL again. And I won't recommend them to friends and family like I have been.
For 3-4 weeks, it didn’t happen. Without a software update to speak of, I successfully switched between sources several times a day without it happening. I can’t explain why. But today it started happening again, switching between the same sources. Until they FINALLY fix this issue, the quickest fix is this:
1. Unplug the TV completely
2. Press the physical power button on the TV 5 times (I do 10 for good measure)
3. Plug in, turn on, switch your settings (mine is Normal, motion off, smoothing off, warm).
4. Wait for it to happen again when you switch sources, rinse, repeat.