I've found out, if you deactivate "NT SMBs", the issue with freezing and ending up with many new folders is gone.

But still not able to delete non-empty folders :-(

If you use the cmd line, you can remove the folders with "rmdir /s <name-of-non-empty-folder"

Please to somebody, who is using snap server within a domain, tell us, if there is also the issue, that deleting of non-empty folders is not possible.