which model is that? I had a similar issue with xz3, it seems to work now ok but I do not trust it much since then. I have not noticed the device getting warm but become unstable losing the network subsystem mobile/wifi and becoming unstable. The trick was to keep the phone in a warm place ~30C for example, fully charge it and flash to android. Kept it running like that for a week and seemed stable, after few initial reboots, then if can be flashed back to SFOS.

I know it sounds voodoo but that's the only way I managed to revive that device twice. I also noticed that if I turn the phone off for some period the problem reappeared.