Restart every 3 min After Battery replacement

I have a iPhone X that starts to freak me out.

Changed dock connector few Month ago, and it started to restart every 3 min after I pressed my code. Tried everything with new ports and so on, but in the end I swapped the motherboard and then it worked.

Now the same phone came back for battery replacement, since I know it's history I was really carefull and didn't even remove display. I just swapped battery and put together. Now it restarts every 3 min again.

Even if I disconnect everything (except the on off and display), phone still reboots.

Any suggestions? This makes me crazy