Bad news/good news to report here. The bad news is that there isn't yet a known cause or fix for this problem. The good news is that Andreas is on the case.
After talking through the situation with Nutlaw, Andreas got a copy of my files (which are suffering the same problem as yours) three weeks ago. I'm crossing my fingers that he'll have something to report soon.
I hear you on the frustration. Our league just had some amazing artwork
generously created for us by knuckler and truthserum. All our owners are thrilled with the results, and it would be a crying shame if we lose all those beautiful new player pictures to this bug.