Are you scaling the collision shape? I read somewhere that the collision shape node doesn't scale correctly in Godot, so maybe that is the issue?
If this is made from a tilemap, are the tiles in the tilemap scaled? I think tiles in a tileset scene have to have a scale of 1 in order to export properly.
I followed this tutorial from the Godot docs when I was learning how to use tilemaps, so maybe it will help? :)