I just had an idea about the inventory bug from a while ago, when I looked at these bugged graphics settings:
As it is obviously stored outdated data from an earlier version that causes it, it might have been the same problem back then. Did you change the item storing system or maybe add / remove / rename item attributes around the time it occured?
Maybe I've played, stored items, saved, exited, updated and stared again? Outdated data is the exact cinda thing that causes such loading issues. And updating the slots by swapping new and old items around could have been the trigger to update those old ones to a new standard...