Eija,
I was hoping for some answers too because my lotuses are doing exactly the same thing as yours. From other emails from people I was communicating with, they told me that it might be the weather got them so confused (I am in SE Michigan). They say just keep them but when the weather gets hot, they might continue to grow.
Also, if the tuber is firm, it should still be fine. If it soft and show sign of rotting, maybe it is gone.
![Sad :(](https://www.worldwidewatergardeners.org/forum/Smileys/smilies_smf/sad.gif)