Why won't my Lightning Flex Cable stay in place?

I have been repairing iPhones for almost two years now, This has never happened before, though. I was replacing an iPhone 8 Plus’s rear glass. Everything was going perfectly. but when I went to reinstall the Lightning Cables flex connector to the logic board, it wouldn’t stay in, and kept popping back out.

Whats strange is, when I just plug the cable into the logic board (Without seating it in) It works fine. But when I put the cable under the board and go to plug it in, it keeps popping out!

Ive replaced this part 4 times now and I am becoming mildly frustrated with this. Can anyone help. Please.