DNS does not work for all ip's

Any days ago UCS-Server (Member server in AD) stopped to resolve names to IP addresses.
Checked all in How-To: Set Correct Nameserver and Forwarder Entries for UCS Servers and found no way to fix the problem.
Only ping to name server (AD PDC) works. Is the a possibility that deals with bind-keys?
Must be a basic problem. Not even the host command works for local server name.

root@mmnucs:~# host mmnucs
;; connection timed out; no servers could be reached
root@mmnucs:~# ping mmnucs
PING mmnucs.IBMMN.local ( 56(84) bytes of data.
64 bytes from mmnucs.IBMMN.local ( icmp_seq=1 ttl=64 time=0.210 ms
64 bytes from mmnucs.IBMMN.local ( icmp_seq=2 ttl=64 time=0.091 ms
64 bytes from mmnucs.IBMMN.local ( icmp_seq=3 ttl=64 time=0.094 ms

Please help to fix it. Thanks

Could find the problem for myself. The service “systemd-resolved.service” did not run and autostart was disabled. Probably in connection with this UCS 4.x apt key expired, no package installation,update, app installation is possible
Had to update the keys after restore DNS function.