7 plus ear speaker not working after screen replacement

Ever since ios 11 came out I have been having issues only with 7 plus. i dont know if its the screen itself or the way i am taking out the ear speaker.

not all the time but 2-3 times. once i put everything together. screen works, even front camera works but ear speaker doesn't work. regular speaker, touch everything seems to be working.

we do have original screens as well. even with oem screens i am having that issue sometimes.

and even if i take brand new ear speaker part out from different 7 plus and install it on customers it still doesn't work.

what could be the reason? is it the way I take it out? or the screen, or its software related?

please help