You might be a great power. I haven't seen any explanation in-game about what confers that status.I made a post about this but be warned the -100 to many great power allies is pretty much broken.
I lost france as an ally due to that malus when i had no other great power allies.
I even reloaded and removed all my minor allies Mecklenburg etc and still lost France as an ally
Cant re ally cant get England Denmark any worthwhile power due to this malus.
am i a great power? nope just playing a trading hansa with a whoping 13k military 3 provinces
Does France have a GP ally? If it does, and you are on the edge of being a GP, that could explain what is happening to you.