My iPhone SE

Try a "forced" restart of your SE:

Press and hold both the Side (or Top) button and the Home button for at least 10 seconds, until you see the Apple logo. When it appears, release both buttons, wait for your device to restart, then test it for a while.

If the issue still persists, have your SE inspected at an Apple Store or Authorized Service Provider: Apple – Location Selector

Regards

Giulio

Perhaps the solutions in the following article will help resolve the issue.

Why does my iPhone SE keep restarting by itself and how to fix it? [Troubleshooting Guide] - iKream