I think your check on the turn was appropriate, and in fact I think you played it well. If UTG had Ad6d or AdKd, which I was thinking one of them may have had as I read the hand as it developed, then your hand was third best on the turn with no chance of either of them folding to a bet. KK was about than 50% to win. Was he looking to check-raise and force out the player caught in the middle? You let him down in that case.

A check on the turn by you, followed by checks by them on the river when the Q hit, told you neither of them had AdKd for a straight. They would not have check-raised the river because they wouldn't be 100% sure you would bet after them. If you had bet the turn and been called by both, what would the Q on the river have meant to you? A made straight?

Anyway, you were paid off. I wonder if that happens if you bet the turn. You end up with the same amount of money perhaps.