'Were' is indeed correct grammatically, but in everyday speech, 'was' is often used. It should be accepted. (For some reason, I'd say 'If I were ...' in everyday speech but 'If he were...' feels more formal).
Either use of yoter before or after an adjective is a flexibility available ONLY TO DUOLINGO employees or they use it arbitrarily.
If I choose to put before an adjective, my answer is marked wrong. And this answer contains yoter before an adjective.