Ok chap, I am not sure what is going on, but the problem is to do with the orange "ground" sprite.
You have up to 15 instances of each ground section layered on top of itself. If you select "ground" from the object folder so all instances are selected, delete it, create a new sprite for the ground you will find it works fine.
Perhaps you have resized the display at some stage, moved ground objects off screen somewhere( if you zoom back you will see stacks of objects off the right of the level, and when you delete all visible instances of the ground sprite from the level there is still 6 instances in the debug menu.
Not the best solution I know. Would pay to try and organise things a little more carefully, name sprite, place them in specific zones outside the layout, keep tabs on how many are in the layout etc.
Edit - The 6 "ground" objects are there, they are definitely the problem but I cannot get them to be visible, or selectable or anything like that.