Cinnamon Toast Crunch is definitely one of those cereals that getting a box is always a huge gamble, because sometimes you'll grab a box where it turns out they were a little stingy with the cinnamon, and like you say, it feels like you're just munching on little cardboard squares - you're lucky if you can snag a box where they were actually pretty generous with the cinnamon, which, of course, makes for a very good box.
And I wouldn't say the cinnamon dissolves so much as it just kind of sinks to the bottom of the bowl, and then you've got to really stir the milk very well to get up as much of it as you can when you slurp the rest of it down.