You can reproduce the email issue though, right? If not, I could see if I can find a save file where it happens for me, with short instructions to trigger it
At this point, if there's no debugger that lets you step through the scripts (I don't know if Godot has that, I don't really know much about how it looks like from a game dev perspective, I just like to see how things work "under the hood"), you could pull out the old "printf-debugging", i.e. adding tons of temporary log messages to see where the code flow is going and what the state of the variables and expressions are at each step. That's tedious, but sometimes the only thing you have available.