Ran into a bug on the first big level, these blocks (the largest chunk and the S-shaped block) seem to be stuck together even though they're not touching.
Shortly after this I tried pushing the big chunk into a wall and the game crashed :( with this error:
ERROR in action number 1 of Other Event: User Defined 2 for object obj_block: PerformEvent recursion depth failure - check for infinite loops, check objects for parenting at gml_Object_obj_block_Other_12