Just checked my hives and it appears there is (What appears to be) brood above the queen excluder in my honey super. Strange pattern in the lower and upper corners of a couple frames. What do I do and how could this happen with the excluder in place?
1. Your queen slipped by you on your last inspection and is now trapped in your honey super. It happens. Has happened to me.
2. You don't have a queen in your hive at all and you have developed some laying workers.
3. It is an upper super of several supers with a separate upper entrance. Bees using the upper entrance have lost contact with your queen's pheromone for long enough that they have developed into laying workers. (Very unlikely)
4. It isn't brood but some oddly formed cells where the bees have capped over pollen or some other substance they wanted to seal up.
I would not guess at whether it is brood or not. I would cut it all open with my hive tool and confirm. If actually brood, I would do a full inspection of my BROOD boxes to see if a queen has been laying down there too. Do you have a properly laying queen, a laying worker, or no brood at all in your brood box?
If it is evident in your brood box that you have a laying worker, then you have a laying worker in your supers too.
If it is evident that you have a queen laying eggs in your brood box, then I am willing to bet you do not have brood in your supers.
If it is evident that you do not have a queen laying eggs in your brood box, and you do not have laying workers laying in your brood box, then I suspect your queen got trapped above the excluder.