[Spellzer]

As the title says my youkai won't level up despite being lower than the maximum level and instead are getting negative x TNL

I did a fight without having new heights after using the class point remover fruit and now no matter how many won fights or massages they won't level up

[Autumn]

You should check if you have the Grand Summoner passive ranked up to 5, if you haven't already.

If not you need to level it, even if you're a bonder or using a guardian spirit.

[Spellzer]

I already have the passive at rank 5

[PantherPrincess]

IIRC your own level matters now too. They cannot exceed your current level.

[Spellzer]

That's most likely it, I just LE'D recently