I found out that the default network id #0 causes the local variable matched_networks in script/dispatcher.lua to be zero. Either you should exclusively check if both network ids are null or raise it to 1 at least. Once I set 1, it worked immediately.

This is "works as designed". Otherwise, any stop that does not receive a network signal will automatically be added to one or more networks.

If you want stations to be in a network without a network id signal, you can change the default in the settings.

I made that change in the 2.2.0 release, see the changelog for the rationale.