Upgrade OX-AppSuite 7.8.4-ucs10

I wanted to upgrade ox-appsuite from version 7.8.4-ucs10 to version 7.8.4-ucs12, because it is recommended to do so, before trying to upgrade to univention-server-version 4.2.5

The version-overview (univention-app info):

The upgrade seems to work and finish’s with the information that the bind9-service is reloading.
After that I can’t even ping the server from internal, but the server can ping my client for example, they are in the same network.
The bind9 service is running and seems not to have any problem!

Maybe any ideas?