Unable to lock and boot loop problem

Hi guys, have some issues with my iPhone SE. First issue I noticed was that I was no longer able to lock the phone with the power/lock button, at first I suspected a faulty button, although it feels fine and I’m able to carry out a reset holding the power and home buttons. After trying this, the phone then gets stuck in a boot loop. Once you connect the phone to a charging outlet or to a PC it starts up normally. I’ve tried restoring through iTunes and still having the same issue.

I fitted a replacement battery about 4 months ago, and have had no issues with it until now. It charges up and holds charge fine, so not sure if it’s a battery issue.