I'm growing several cassabanana plants South of New Orleans. Most of the fruits have started blossom end rot once they get about 4 or 5 inches long. However, I have one that set properly and is now about 14 inches long and it looks healthy, still growing. I have seen at least a dozen that developed the rot and have fallen. There are dozens of small fruits that have not flowered yet but are growing fine.
A lack of calcium is the reason.
This article will help you.