* update: I have replied to your initial response, not subsequent posts *
Sorry, I just don't have any more ideas right now, only to check your IIS and PHP error logs and look for some clues (but chances are you will get some generic timeout error when you hit pre-configured limit).
Market pages do pull things via market api dynamically, and maybe there is some issue there team is not aware of yet, maybe even tied with specific conditions that needs to be met, don't know really.
In any case, keep it monitoring for the time being.
Regards
dev101