Hi Pascal, I'm sorry about the issue with class-sync not working correct.
Would you be able share the error message with us? Specifically which class is duplicated & what component were you using? We can look into this further.
Additionally, one issue we're aware of is webflow files with duplicate top-level classes of the exactly same name. I'd recommend searching the webflow styles tab for the class name mentioned in the error message to see if that's the case here. You can delete one of the duplicates to fix the issue.
CC
