As I said, not much is known about this topic, and a lot more research is needed before anyone can say what's right and what's wrong with it. But if you feel there is something really wrong with it, please turn to the bugs forum.
but i won't expect a big random factor with it, when i was U21 coach i noticed the experience ups from time to time and all 21 have XP 3 at the end before the first one get XP 4(i believe this jump was made by two player who played in the past nearly every game).