To reproduce:
1. Open attached Unity project "BugReport.zip"
2. Open "Steps" scene
3. Inspect that yellow steps have mesh colliders and are higher than pink steps with box colliders
4. Go into play mode
5. Try to climb pink stairs
6. Try to climb yellow stairs

Result: Character controller is unable to run straight up the pink stairs, however, it is able to climb yellow stairs despite the fact that they are higher than pink ones.

Note: Changing yellow steps' colliders from mesh to box, character controller is no longer able to run up.

Reproduced on: 2017.1.2p3, 2017.2.0p4, 2017.3.0f1, 2018.1.0a7