Depending on variety, it could be part of the trigger for ripening? Or perhaps the plant has aged so much it can't support all of the fruit, and is trying to abort some of them?

Might be the latter. The fruit set in September, and the plant is looking sort of peaked, so probably trying to die.

D, probably the banana is old and already went through some cold days that we had.

I have another banana growing in my yard, the one that I had about the same time as yours is long gone and taken out , giving room for other stalk to fruit.

Since we are talking bananas, last week I went to a far away botanical gardens and I saw this that look like a banana but it was not, the flower was huge!

Silvia