Home button feels sunk in and sticks

I replaced the screen on my first iPad Air ever. Before closing it up I did the usual QA check. And after closing it up I did it again. All was well on my bench. Two days later the customer contacts me to tell me that the home button was sunkin and sticking. Sure enough when he brings it back to me, it's sunk. I removed the screen and compared it to the old one (which thankfully I had not tossed yet) and there was a missing cushion. I replaced the cushion and sealed it again. I test it and it works fine. Call the guy to come get it and show it to him while he is there.

He calls me an hour or so later and says it still has the same problem. So I offer to replace the screen at no cost to hime. I order from a different company and make sure that I odrdered the screen with home button installed!!!!

I put the new screen in and transfer the cushion. Sure enough after a day of usage, the fellow calls me AGAIN and says the same thing is happening.

I know this person, not that well, but we travel in the same circles so I know he's not putting one over on me or anything like that. The problem is legit.

Anyone else have such a problem with an iPad Air? What did you do to resolve it?

Thanks,

Norm