Synology: MinimServer only with internal IP

[MofoDesign]

Hi,

I have upgraded my Synology server and the Minimserver is actually running perfectly. However, I can only reach it via the internal IP address and not via the external address as before, which is also called up automatically when I click on Minimserver.

I have checked the settings in the router and port 9790 is open. Could any Synology settings be wrong?

After hours of searching I can't find a solution.

Kind regards
Martin