Havent used the spell much until recently (mostly just for the hound and thats a clicky) but on my caster Ive just gotten high enough to use it and nothing is slowed by it.

Ive used it on slimes, kobolds, gnolls, wolves, hobgoblins, iron defenders, humans and orcs at this point and the completley ignore it........... although it does provide concealment cover.

Ive dropped the spell until a fix shows itself.