Loading new variable library is not working (AI 2025)

I have round about 25 variables linked in my file connected to different variants of a Design. When I'm loading the variable library with exactly the same columns but new cells or other content within the cells - i get this error: (translated from german:) The filter cannot be completed, because an unknown error occured. I dont use any filters in my design. Also the first loaded library is working without any issues - the content is changing according to the CSV data set. I tested with lesser variables - but got the same error.

Also i cannot find the error protocol to get more information on this specific error. Can someone help?

Thank you!