I have a similar problem, Q7FN from 2018. In my case, the TV gets to a reboot loop after 30minutes/1hour. I am from Brazil so room temperature here is pretty high (30-35ºC) unless we turn on the AC. First thought: thermal paste problem. Opened TV, found a black plate (passive cooling) attached to some components, one of them a processor with thermal paste, I thought, bingo. Thermal paste was hard as stone, nailed it! Changed the thermal paste to the same I use on PC, arctic mx-II or a noctua one, don't remember, retested, problem persists. Second thought: one connect must also have some passive cooling with the same style, tried to remove the board, won't come off, glued so hard it bends the board if I try to remove it without pre-heating it. Left the one connect box away from the TV and turned a FAN on pointing at it's carcassless body, problem remains. Replaced the fan from the one connect to the back of the TV panel with it's carcass still on, problem stops. So in my case I believe the problem lies...