Bad news!
I have been working the entire day on a prefab (this time without global variables) and the bug is back.
It started with one action, then suddenly more of those were affected and now the prefab is completely corrupted. No matter what I do, I can't make it work again. Not even by replacing the states, because I replace one and the error appears in an another.
I think this time it happened after I added another variable in the variable tab that then sorted the entire list alphabetically and this fucked it up. Can't say for sure. But damn, the bug is still here.