Responses
Is this a spoiler from the novel? Cause I don't think this is the case. The mc and his rich friend who became a leader of a guild went to a bunch of dungeons with no problems, and the dungeon with the other a-rank team went well too. It just seems that he is shit out of luck and this is the second time a dungeon had a nasty surprise. Didn't he have a bad feeling about this one before they entered? I think, that wether he entered or not, this would have still happened.
So, anytime he enters a lower ranked dungeon than himself it seems to automatically upgrade the dungeon with more difficult creatures, or just raise the grade of it completely. I wonder if anyone on the outside noticed a change in the gate once the group entered.