Share Point Online - mail distribution list (security group) name changed

Hello,
i have a really tricky problem in SharePoint Online.
Since we introduced SPO, we activate the security group option for a mail distribution list.
The permissions worked fine for the persons, who are members of this distribution list.
Last week, we changed the name of the distribution list.
Now we have the problem that the security group in SPO has still the same name, but the users has no access to site. 
If i delete the permissions for the group, wait and add the permissions again, its the same problem....

When i add the group on another sharePoint Online site, it works fine, the new name is displayed and the users has access.

Thanks for your help!
kind regards
Silas