How to reproduce:
1. Open the attached project ("steel-flood.zip")
2. In the Hierarchy Window click on the "RoomsFactory" object
3. Observe the collider in the Scene Window
4. Enter Play Mode and using the arrow keys on the keyboard move to the right
5. Observe the Player's movement

Expected result: the player object walks on a flat surface and doesn't fall through the collider when walking to the left
Actual result: the player object walks on a ramp-like surface and falls through the collider when walking to the left

Reproduced in: 2019.3.0a6, 2019.2.0b6, 2019.1.7f1, 2018.4.2f1, 2017.4.28f1