[Ammako]

You're running :Hide() on the nameplate itself, why?
The nameplate already disappears when unit is removed, that part is redundant, and you're not actually hiding the iconframe. Meaning, once the nameplate gets reassigned to a different unit, it is still anchored to it and will still appear, even if the character is of the wrong class.

[I wrote a thing here that I realized would not work, edited out]

Also, not related to the functionality of your code, but you are creating a new frame every time a nameplate appears. You should only create one per nameplate. Efficiency reasons.