Signaling between instances never seemed to work for me. But I'm wondering if it's just another counter intuitive thing I'm missing. Just like when a person adds a child instance (spawn) in their code, they also have to add that instance within parameters of the node inspector.
Viewing post in Technical issues you ran into while developing
Signaling between instances that don't belong to your tree shouldn't really work properly.
When you instance a scene then you must add it to the tree with add_child(variable_with_instance)
Maybe that is the source of the problem? If you upload a project with the problem I could take a look and help you understand it.
Damn I never had an issue with signals, but this was not clear in the documentation. I have a C# background and I've been kinda treating signals like events. I guess it was a coincidence I didn't have any issues with them, then again there were a bunch of bugs in my project and I used signals a lot so maybe this was the issue with some of those bugs.