Both times are on you. A person may not find a movie engaging, but sleepiness is not caused by a movie. Just the way you describe the movie sounds like it didn't offer much to you, which is fine. Also, 2nd acts are notoriously difficult to pace being bookended by the 1st and 3rd acts.

In this particular movie, there are a lot of character arcs so a lot to accomplish and cram in there. For what it was doing, I thought the pacing was excellent.