I sent an email with the pic to AGP Arms and received this response within an hour:
"The problem you have encountered has nothing to do with temperature. It is a problem that is isolated to a certain batch of mags we had molded. It’s a long complicated story as to what is wrong with them but rest assured it is an isolated batch that we have disposed of. Someone at the molding plant was fired over it if that makes you feel any better. If you would send me your address I’d like to send you out two new bodies today. I think once you have tested these all your reservations pertaining to our quality will be put to rest."
I'm very impressed with the professionalism of the response from AGP Arms and I look forward to testing the replacements. I'd rather not support Wraithmaker and the 20-round drum, lest the Saiga 12 platform go the way of the StreetSweeper. So if these 10-rounders work, they are enough for me.