Problem with El Captain (Server 5.1.7) and Permissions Management

Hi Everybody,

i have a big problem with our Mac Mini Server (El Captain) and the Server Program.

Since a few Weeks the Server didn't hand over the permissions from Folder to Folder.

e.g.:

Mr. X had the permission to read and write in a folder.
Mr. Y too.

Mr. X create a new folder an save something in it.

Mr. Y didn't have the permission to read or write in the folder Mr. X create. But he should have.

Did somebody knew what the problem could be?

Thanks

Greetings from Germany

Chris