At first glance this look correct. 

What is the exact issue? 

Does the Incident Task actually have a reference to an Incident? 

If yes, is the short description and assignment group populated in the linked Incident? 

@Klaus Schacht 

it should work fine if your incident task gets created and has incident field populated.

If you are using parent field then use that instead of incident field

If my response helped please mark it correct and close the thread so that it benefits future readers.

Hi @Klaus Schacht ,

are you using incident field or parent field for linking incident task to the incident?

if it's using parent field for linking update you BR condition and values with parent instead of incident

Please mark my answer as helpful/correct if it resolves your query.

Regards,
Chaitanya