No real "bugs" (admittedly I didn't go out of my way to find them either), more-so game design issues/choices I personally disliked.
The difficulty curve felt a bit all over the place; there's a point where like 8 Meetles and portals suddenly spawn all at once, but right after that it reverts back to one spawning spot with only a few portals that are so out-of-the-way they aren't very relevant.
I also mildly disliked the fact the spaceship vanishes for a while when a single Meetle drops into it. Lost a fair few lives dropping two of the same color in at once. I suppose it's part of the chaotic nature of the game, and that's fine, but you're already having to constantly manage your Meetles to get them all safely down and into the right ship.