AI missing their pit boxes (as I tried to describe in my post above) is caused by flat tyre - they go pit in for to get it changed, but they don't recalculate their stopping distance(as it is obviously longer with a flat tyre up front) and overshoot the box.
Started 3 lap AI (XFR+UFR) race at AS Cluv REV again and after they all made mandatory pitstop, I set laps to 60, so the AI drivers had to pit in for fuel every second lap... and they managed to spot in the correct place every time
So, they need to take into account their tyre condition not only while racing, but also while pitting too (if they already do that, it must be something else that causes problems).