Try this:
SELECT id, attempt, seq_number, question
FROM question_states qs
INNER JOIN (SELECT question, MAX(seq_number) seq_number
FROM question_states WHERE attempt = 374 GROUP BY question
) AS A ON qs.question = A.question AND qs.seq_number = A.seq_number
WHERE attempt = 374
OR
SELECT id, attempt, seq_number, question
FROM (SELECT id, attempt, seq_number, question
FROM question_states WHERE attempt = 374
ORDER BY question, seq_number DESC
) AS A
GROUP BY question