Strange. Have you tried to click "Next" when the level is completed ? Maybe there is indeed a bug somewhere.
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Replayed it, now it let me. I had to change my rating, because i really loved the stacking of objects, really fun and one of the best games i tried this jam, it would easily be the best if you had more time to polish it. Few things that really frustrated me: No depth in visuals - it look really cool and i love the visuals, but if you made it so that you could see at least somewhat the depth of objects or the edges, it would make the gameplay (at least for me) a lot better. Also, the physics were sometimes kinda strange. Other than that, love it!