I understand why you removed this reference class, but is there a way we could keep the animation and de-couple it from the base .tip-error styling? My recommendation would be to have a class of is-showing (with the @extend .anim-fadeIn associated with it) and a class of is-hiding (@extend .anim-fadeOut associated similarly). 

Would you mind adding the management of those two classes to your JS logic and trying it out to preserve the animation in the UI?