If you don't mind my asking, what mane .png did you use for the preset? You want to make sure that you use this file (FeralHeart>Media>Textures>Masks):
I've been experiencing this problem in the last couple of days. I created a preset for my character, but it seems the mane is not rendering fully. However I can see full manes rendered for others. This problem happens on both the full and light version of the game.