My issue was definitely temperature-related. I eliminated all of the other variables (no Fire Stick, no remotes with low batteries, removed all cables except HDMI which I replaced with a new cable, reset TV to factory settings, tested a variety of video sources) and all it took was moving the TV away from the wall a foot or so so that air could flow behind it. Instant fix. Haven't tried replacing the fuse yet as suggested, mainly because I couldn't find one easily accessible (i.e. not behind the hatch that the power cable goes into.)