Ok a lot of units still get stuck on CSGs. This was suposed to be fixed but is still happening on a lot of maps. I don't wanna start spamming the topic with screenshots of units stuck because i will make it look very sad. This also makes the balance worse because units like bots are much more likely to get stuck. Air obviously has no problems and is already totally awesome so its a little lame that the guy with the easymode armycomp ( yolo fighters and bomber deathball) also never got a single stuck unit where the guy who makes ground constandly has to re-send forces that they already did send, but just got stuck....
I think the path finding is a general problem rather than balance topic. You should post this thread in general discussion, and there are also more people who can see it.
I got the impression that pathfinding only breaks down in later stages of a game. Usually there aren't many glitches in the beginning, but if you get to a point where many units running around pathing starts to break and then gets continuously worse with increasing unit counts. Additionally, if you try to reproduce pathing behaviour in a "clean" game it will not show up. It almost looks like the pathfinding algorithm has some kind of time quota per sim tick, and if this gets used up it will switch to the fallback behaviour (AKA "just run in the direction of the goal").
In my experience, units may not bypass the occluder which blocks between the unit to the goal. But if you use shift to give the units a sequence of midway points, they still can get the goal. This path finding problem mainly occurs in longer distant movement.