As adjectives the difference between atypical and erratic
is that
atypical is not conforming to the normal type while
erratic is unsteady, random; prone to unexpected changes; not consistent.
As nouns the difference between atypical and erratic
is that
atypical is (pharmacy) an atypical antipsychotic while
erratic is (geology) a rock moved from one location to another, usually by a glacier.