Nectar or syrup that has not been capped can ferment.

But even capped honey can absorb moisture from the environment, the cap is not water tight.

There is no mold known to man that will bother the bees. They can deal with it.

If it's really bad (stinky) scrape the bad off leave the rest give the bees a start, the bees will rebuild and quickly if needed and conditions permit. I'd leave any capped honey intact, the bees will probably first pull the honey from the frames and redistribute it in the hive when you give it to them. The house bees will clean all the cells when they are able/needed.