Can´t enroll iPhone(s) with Apple Profile Manager

If I want to maintain a device in the "Profile Manager", then I get the following message in the "devicemgrd.log":

Unassigned Device Enrollment Program profile(s) from devices: S/N, S/N, S/N (see picture above)

The task is then stuck under the active tasks in the "Profile Manager".

So I can no longer roll out new devices.

Does anyone have an idea what I can do ?