If you were keeping sugar water inside the hive all winter, along with the heat that the bees produce, it's possible that the sugar water that the bees decided to store fermented.
You might want to test that frame in the top picture for AFB. It looks from my prospective that you have capped brood that are discolored and sunken in. Maybe it's mold, but better to be safe than sorry.
Best of luck with it.