No sim after screen replacement

I ran into this issue before but honestly can't remember how to fix it. I just replaced the screen/lcd frame on a customer's HTC One m7 and everything works perfectly....except for it reading a sim card.

Here's the kicker..when it's removed from the back housing and everything else is still in tact it read the sim with full bars. But as soon as I put the back housing on it goes back to reading no sim. I've tried putting tape over the connection (flex to zif) and taking out the main board and re positioning it/aligning it. No success.

If anyone's ran into this issue or has any tips please! Thanks!