iphone x shuts down by itself

Hello there. My iphone x turns off by itself, sometimes the apple logo comes up, it does not hurt at all, sometimes it turns on. Sometimes it resets. Sometimes it turns off and reopens and turns round on the black screen, it stays like that, I have to reset it myself. I showed it to a lot of repairmen, they repaired it and gave it back to my father, the phone came and I encountered the same situation again. The phone is getting hot, but only on the bottom left of the camera. In general, it happens when it gets hot. What is the problem with this? Do you have any information?