Removing bump when going through two adjacent colliders

Hello,

I'm a newbie in unity, and had only finished the roll-a-ball tutorial a few days ago. To challenge myself, I wanted to expand the game into a 3d platformer-esque game, creating a "level" out of 3d cubes and other objects

However, i noticed that sometimes, when the player ball goes through two perfectly adjacent colliders, a small 'bump' up may still occur.

Several search attempts has shown that this is a pretty common problem regarding ghost vertices, but I've yet to find a single working solution. I don't think a charactercontroller will work for such a physics-reliant minigame, and some other solutions that involve editing "Min penetration for penalty" to 0 no longer work since in unity 5 it has been changed to default contact offset (which has to be strictly positive, apparently).

Some other solutions involve replacing everything with a single solid collider, but as you can see from the screenshot its not really feasible (plus it's not really the most elegant of solutions either)

Alternative solutions and help will be much appreciated, thank you in advance!