Hi @Jonas, and welcome to the ODK forum! When you have a chance, I'd encourage you to introduce yourself here. Doing so helps build community!
survey.csv
contains a group whose name is group_ smis
(with a space). However, spaces aren't allowed in field names. Have you been able to use this XLSForm successfully?
The name of that group seems to be the cause of this error message. However, I also see non-ASCII characters in the CSV files. For example, the label of field note2
contains the text "Centre National de SpÇcialisation sur le maãs (CNS-Maãs)", but Ç and ã are not ASCII characters.
Hope that helps!