The issue with unlootable GCM chests isn't resolved and isn't limited to just the top left treasure room. I've done a couple of GCM red runs, and the issue persists intermittently. I was only able to loot that chest one out of 5 runs I've done. The chest in question is the top left chest in the top left room. The second unlootable chest is the top left chest in the bottom right room. This chest has been unlootable since I have started doing GCM runs over a year ago, but had never been mentioned for bug fixes to my knowledge.