It was easy and replicatible. I've done it on map 37, it appears these blocks don't have correct collision.
to do it, go past all the alien plants, and reach the area with the bat on the first platforms. The, grapple into one of the blocks and you get inside. You are able to get out by jumping and moving to the right.
EDIT NOTE: you can recreate this on all the platforms on this part
NEW EDIT NOTE: you can do this on ALL platforms in all gamemodes