Okay, for UMP25 I will start out by saying I didn't see the play!
Perhaps the check swing was not a "half swing" as the rule requires. I have seen many catchers ask for a check swing appeal when the batter barely moved the bat or moved his shoulders a little. The catcher, busy catching the ball, thinks that the batter made an attempt, when it is obvious to everyone there that he did not even come close to a "half swing," much less an actual attempt.
I don't ask my partner when it's obviously not close to even a checked swing, even in OBR. I've never had a coach insist on asking on one of these obvious non-attempts.
Also, the rule states that the manager cannot complain about the ball or strike call, but can only complain that the umpire did not ask for help. Well, go ahead and complain. That's all the manager can do is complain. There is no other proscribed penalty for the umpire.