Reason that battles get Desynced?

[pyrromanis 70]

Ok, after a lot of battles online and talking with my opponents after a desynced battle I came to the conclusion that each side seems to get different damage rolls on hits. I've got numerous times the scenario where a mon survived a hit on the one side but died on the other due to each side getting different damage rolls thus making the battle desync. Usually you won't get the difference since residual damage are fixed % and most hits are clean OHKOs, 2HKOs or do very little damage to make the difference visible. It becomes more obvious with medium damage rolls since the more you trying to weaken a pokemon, the more different rolls each side gets making the pokemon end up with very different HP between the 2 sides. Also damage rolls that have an X% to OHKO/2HKO can make a difference and end up desync the battle