This has happened to me twice.
First time in late March. I got my pixel 4 xl in early November in Australia. Google support told me to send back my device, here in Canada, and got a refurbished unit back with RMA. All they asked if if I used the original charger, which I did, and to send a photo of the device.
Same story now in early July.
The first time I was actually worried for battery swelling, as I had read it could be a possibility on Reddit, and half of the glass plate was coming off.
The second time around it was just the top corner, opposite from the camera side coming off. It didn't seem like this would be a battery swelling issue, although I contacted Google and they offered to replace the device again.
I considered selling my 3rd unit ( 2nd refurbished unit sent to me) in its sealed package and switch to another phone... But I couldn't do it!
My first unit always had a case on and it was in mint condition, no scratches, nothing. I never had a case on my second unit. It may be the case doesn't do any difference at all, but only covers up issue.
@Sean Docemo , I would get in contact with Google support again, on both of my occasion they were quite quickly able to offer RMA. As Mustang said, try again until one agent does something about it!