wisconsinbananas

So I've had two banana flowers emerge, appear to get stuck, shrivel, and rot, all in the last 3 months. Now my THIRD banana has shot up a flower and that one is also sticking in the opening and showing signs of rot. Up until then all 3 have looked perfectly healthy. No obvious rot, not black streaks, no spots, no holes. Two are truly tiny cavendish type, the most recent is a dwarf cavendish. I have them direct-planted in the ground, consisting of about 1 1/2 feet worth of compost and potting soil, with good old wisconsin glacial till further down. They are kept in a greenhouse at 60F minimum (with several grow lights for the shorter light season), and the vents open at 85F. And i've had them for 4 years without issues and gotten several nice clumps of bananas. I give them an occasional scoop of chicken poop for fertilizer. I have no idea what could be wrong.