Enterprise Portal + Launchpad: Applications do not start

Dear Experts,

after upgrading the backend system (HCM) to EHP8 we are facing the following issue:

1. Starting SAP-Portal

2. Launchpad is displayed

3. Link in Launchpad is selected.

4. Loading animation is shown, but nothing happens. Application won't start. It is the same, when the launchpad entry is a URL/Link.

It seems as if the communication between Portal and Backend works but not vice versa.

Developer tool in Microsoft Edge shows, that there seems to be no response from the backend.

Any ideas, suggestions on how to solve this issue or how to analyse it further?

Thanks in advance, best regards

Chris