Hi, alex. Do you have an oven thermometer? If you don't, I suggest you get one. Ovens, even brand new ones, can be off by several or quite a few degrees. Before you bake your cakes and breads, do you preheat the oven? This is an important step in baking. Some ovens can take as long as 20 minutes to preheat, which is about 1/3 of the time that banana bread bakes. If you're not preheating your oven, this could explain why your banana bread is undercooked.
So, get and use an oven thermometer and always preheat your oven. I would imagine you will get different results the next time you bake.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!