Hello Bernd,
Thanks for the inquiry. Can you please confirm if the new Technicians role assigned to the group of agents is the only Role associated or is there others ? You may be observing an issue with multiple Roles assigned and the other role may have Full control whereas the new Role does not allow this. The Roles are accumulative so you may need to exclude a Role where there is full control to the Knowledge Base.
Please let us know if you have continued difficulties. You may prefer to have us look into this further by opening a Support Ticket.
Thanks.