If you are a non-US dialect of English, unfortunately Apple has made those months have the period at the end. Try adding US English to your language list and it should work after that.
I tried this now and it worked well. The problem is only that my System language is German and I would need to change it permanent to english to establish the hazel change. So this is not a option for me - is there a other workaround, maybe to use the month with the "..." token or something like that? Thank you again for your help.