There’s nothing amiss. The physics engine has a thing called “slop” where it adds a slight gap between objects to make the simulation more robust. Anyways, this isn’t controllable in construct.
A solution is to make the collision polygon slightly smaller so the gap isn’t visible. A more exact solution would be to have an a separate object pinned to the physics object. Just add 1 to the height and width.
At least that’s an immediate solution based on what we can do.