Dungeon Attack Count Limit?

Dungeons that I could barely participate in before have been appearing in large numbers this month for some reason. This is my first time really diving into them. Previously, I'd either be defeated by the 5th or 6th mission clear, or the time would run out. But this time, I cleared the '1 attack mission per 30 minutes of play' 14 times by yesterday. ...And then the missions stopped updating. Another dungeon I'm participating in also stopped updating, so I calculated the attack counts and it was also 14 times. Is there a limit to the number of times a mission can be cleared? With strict participation requirements and few players, isn't it impossible to defeat them... There are still 39 days left, but if the limit isn't lifted, I have no way to attack anymore...😢