Power button stops working after trying to shut off the phone?

Hi everyone, I’m having some trouble with an iPhone X that has had the rear glass, battery and LCD replaced.

the power button works fine to turn the phone on and to lock/unlock the screen, but when I hold it down along with the volume up button to turn off the phone, it won’t work. after that it won’t even work to lock the screen and apps won’t open when I click on their icon! Any idea what the problem could be? The phone is running in the most recent iOS 14.2

Thanks in advance

Update: the lock button will work to take a screenshot but not to turn off the phone