PolygonCollider2D colliders are incorrectly generated from sprites with 90 degree corners.

2) How can we reproduce it using the example you attached.

In the test scene, the sprite on the left has an incorrectly generated collider. The sprite on the right has had the sharp corners cut off, and has a correctly generated collider. (The incorrect collider can be corrected by setting the detail to 1.0, but that shouldn't be necessary, especially since the correct collider is actually a more complex shape.)

1 Open scene test
2 Select "Shape 1" in Hierarchy
3 Remove and add Polygon Collider 2D - the generated collider is incorrect