That is interesting because up to now, the TOP corners are the tight ones. It is the bottom corners on most of these cases that are the problem.Joined the board just to say that I had the same issue (well, my dad did). Not long after buying him the Apple iPhone 12 red leather case, he asked me why his phone silenced itself. I noticed that the mute switch was set to silent, so I switched it back and told him that was the problem. He kept coming back to me with the same problem, multiple times a day. Upon investigating I discovered that the phone pops out of the corners slightly and sometimes hits the mute switch, thereby silencing the ringer. I would add that he is extremely careful with his phone and never drops it nor throws or slams it on any surface.
It's so frustrating because it's such an expensive case, and it's fantastic in every other regard. I really want to love it. Oh well, I will be returning the case to Apple.
So, the corners popping off is contagious disease affecting the other corners too!
IMO, use just a small dash of Elmer’s glue (kid’s glue) on the troubling corner