collision detection – slightly interlocking colliders; Any solution?

Consider this simple scene:
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In Unity3d, the colliders cross slightly. As a rule, this is not a problem. However, I want to create a custom character controller using a box collider and not a capsule collider. In the scene above, the floor is divided into 2 objects, each with its own collider. The game controller has its own box collider.

And the problem: if the box collider moves forward, it clips with the seam on the floor, even if the two objects on the floor are the same height. The box will stop moving as if it had hit a wall. If I keep adding strength to the box, it will never progress. It will get stuck on the seam – this only exists because the box is slightly inside the first floor collider, and it will hit the second collider from the ground like a wall.

This only happens due to clipping of collisions. With most game controllers, a capsule collider is used and therefore this problem does not exist.

Is there work around? How can the box move smoothly on the floor without colliding with the seam?