iPhone XS Max restart device every time after update

Hello I would like to ask you some questions. Just when someone asked me that the iPhone XS Max suddenly went off like the battery ran out. When disconnecting the charger When the charger is plugged in, it works normally as if nothing happened at all. And this symptom has disappeared since iOS 15.0 update. It happened because of what reason? At the moment, it's seen by many people. People who use XS also have it, but I ever asked Apple's support and they responded. It's caused by software. Is it possible that it's caused by hardware? This symptom is all at the same time. and such symptoms healed at the same time Both replaced the battery and cleaned the device, not lost. Is it possible that it is caused by hardware or have to wait for apple to fix this software only?