Is this a subject verb agreement error?
I think the teacher thought there was an error because the sentence appears to have no subject.
Stripping out the unimportant parts, here is your sentence:
According to Political Research Associates, recorded hate crimes increased.
You can see that the sentence has a prepositional phrase According to PRA but no subject for the verb recorded -- except that recorded isn't actually the verb, it is part of the actual subject recorded hate crimes for the verb increased.