iPhone keeps rebooting. I know the problem, don't know how to fix it.

My iPhone 6 plus screen broke after falling. I replaced the screen and worked perfectly fine. A week after replacement, phone starts rebooting and stuck in a loop. Tried multiple ways to get it out of the loop (soft reset, hard reset, recovery mode etc) but couldn't.

I took it to the technician and said battery needs replacement. I replaced it and worked fine for another 48 hours and the problem happened again. Took it back to him, now he says it's something with IC processor. Tried another technician said it was software, and another said possibly processor. I ignored them all.

Then I noticed something, when I apply pressure at the center back of the phone while it's booting, it works. It worked for the past 48 hours, then got into boot loop again. Applied pressure again, now it's working fine, until I don't know when.

What can be the issue?