Things like trees spawning too close together, like diagonally at chunk borders, and floating leaves. I also found a half a villiage house, screenshot attached.

So is Primitive Mobs the only mod you have? There is only one generation thing PM adds and that's Mimic Chests which is a single block. Are you sure this is caused by this mod? It sounds unlikely.

I have forge.

Is that an older world from before getting a new version or installing primitive mobs? Older worlds might have this issue but thats not unique to Primitive Mobs.