Hi megatronx. If you zoom in to a ridiculous amount you will see that the corners (where your rotated black tiled background objects meet the flat tiled background object ) are not perfectly aligned, causing jagged edges that are "catching" the bottom corner of your platformer objects.
I wish there was a setting for the platformer behavior to set how sensitive/forgiving the behavior was about such incredibly tiny details/imperfections in the terrain.
To me, this is at such a high resolution it really should be considered a bug....
However, the solution is to not use tiled objects like this for angles... you should design tiles (using the tilemap support or Sprites) that, when using snap to grid are guaranteed to line up perfectly and not cause such jagged imperfections in the terrain.
Cheers,
Mike