"I hope you followed me despite the rain."
Translation:Spero che tu mi abbia seguito nonostante la pioggia.
the past participle with the auxiliary "avere" has only to adapt when a direct object pronoun in the third person singular or plural is used (lo/la/le/li) in the other cases of direct object pronouns (mi,ti,vi,ci) it's optional and nearly never used.
So, it's not wrong but really less used.
spero che tu mi seguissi nonostante la pioggia not accepted 6 Aug 2017; reported.
Subjunctive imperfect seems to me to be just as valid as the compound subjunctive past - especially since Duo recently marked me wrong for failing to include the auxiliary verb in my English translation in another exercise.