My first thought is that it dried out one day, but it's hard to tell without a picture. Do you have any pets. If a cat pees on a potted banana it will do something like that to the plant, and you'll have to wash the corm, pot, and change the soil. What ever it is sounds soil related, so changing the soil would be a good course of action.

Basjoo can do wonderfully in a container, however a few things I learned over the years.
Container grown Basjoos tend to do well if they are indoor plants, Then taken outside in a shady environment on warmer to hot days.

If a Basjoo stays outside in a container under bright sunshine, soon, they will become rootbound. A extremely fast grower, the Basjoo sounds rootbound and is searching for more room to grow.

You mentioned you have pups, well, this is a good sign that you are meeting every condition the banana needs to not only grow, but to have pups to expand. Now, its looking for more room as the pups are growing along with mom.

My remedy would be this, get a larger pot. Or, you can overwinter in the house or garage, a cool dark room. Then, I would suggest in the spring you plant this Banana in the ground.
They call them Banana Plants, I call them small trees.