The restart of the service pxgrid and network-design solved my issue. I did not had to change the certificates because there wasn't an "UNTRUSTED" message in the log.  Many thanks @Martin Grimm 

Hi, I have exactly the same issue error message, after running this connectivity over a long period. My DNAC is 2.2.2.9, my ISE is 2.7 Patch 2. I checked the whole config again and startet the services new, but get still the message. Anyone have some...