IGA 3.7.3 - FQDN of OSP has changed

Dear Forum,

in my lab environment I have installed IDM Applications and OSP on one Server and IG on an other server. 

The setup was working, quite well.

After a while I changed the IDM Applications and OSP to run behind an Apache proxy and changed the FQDN as well.

Access to IDM Applications through the new FQDN and an url like https://newserver is working as expected. 

Since IG was using the OSP on the IDM Application Server by the URL https://oldserver:8543 I know I have to change the IG configuration, but this ain't work

First, I started the configutil provided by the IG installation and changed the OSP server in the authorization configuration.

But after pressing save the configutil gets stuck - I waited for several minutes, but it did not terminate.

Checking the ism-configuration.properties on the IG server I found two parameters still referring to the old OSP URL https://oldserver:8543, and I changed those parameters manually to https://newserver - but with no success. Accessing the login page, the browser is offering only a blank page! Using the browser development tools I found, it still is trying to access https://oldserver:8543

Can anybody provide some ideas how to fix the IG setup without reinstalling the whole server!

Kind regards