Find Session does not find Session on same computer

When I search for Sessions (after hosting on same computer) in the engine, it finds nothing. Some months ago it worked! Also the shootout example doesn’t work, just finds nothing.
But I want to test it in the engine. Any ideas where the problem could be? I’m completely out of ideas.
It’s like this with all engines I have installed and the old projects, that were not changed in meantime, don’t work anymore as well.
I use Subsystem NULL, LAN is enough for me at the moment.