Looks like you have changed your server name while WDM was installed or moved to a different domain.
Download the “WDM SQL Queries” from https://technicalhelp.de/ and look at the Server table of your WDM server. If it does not contain the correct value, delete it completly and do a reboot. Also check the LatestHFLevel and correct it if one is not the same as the others.
If this is not fixing your issue edit the DB and check the Install table also. Do not delete the install table as this one will not be recreated the value automatically. Correct the name field here to reflect the FQDN of your server.
CG