To my understanding, it happens if the game's rendering a bunch of complex models at the same time. If you play with just two players on the map, each with a default Brawl model, does it still happen?
Yeah, it happens in 1v1 matches (offline) with default character models. When I remove my SD card (and codes are still loaded), it doesn't happen.
The question is how much does the game skip frames... there are 2 instances I can think of.
I'm not sure about the exact number of frames, but it's pretty noticeable. And I mean, I'm just using stage textures from the vault when it happens. For example, this one
Come to think of it, this video looks a little choppy... but in the actual game, it would be even worse than this.