Ok, two issues going on.
Joelel, mildew (or mold) on combs is common. Stored comb gets it, comb that is not being actively maintained by the bees outside the cluster over the winter will get it, the boxes and frames will mold as well. Very common, considering there is moisture as well as traces(or more) of sugar on the comb it is to be expected. The bees will clean it. But if you are getting white and black pebbly things on the landing board, then see the next paragraph.
Lone, your picture is in fact of chalkbrood mummies (yup, a fungus). Whether the fuzzy stuff on the mummies is the fruiting bodies of the chalkbrood fungus or mold doesn't matter too much. But chalkbrood doesn't cause the comb to mold, only the bee larvae. Chalkbrood can be caused by excessive moisture, the bees can usually clean up an infestation, but occasionally if the hive is mature the queen will need to be replaced if it doesn't go away.