Why my friend's phone automatically restart when she turn off the bluetooth?

The bluetooth automatically turn on when she open the google app and when she will turn off the bluetooth. The phone will automatically restart. Any ideas how ti fix this issue? Is it in software or hardware problems sir?

What phone?

Welcome to Android Central! Does it happen in Safe Mode? If so, then it's probably a problem with the firmware or hardware. Depending on the phone, you might be able to reinstall the firmware to see if that helps.