In my experience its not about "luck" or some kind of random thing, but instead formation arrows and something Ive figured out ... Your players "learn" to play together in a certain way against other teams, if you change your formation settings and stuff like attacking area mentality arrows, etc. Your players have to Re-Learn how to play like that, against a strong teams comp, your "new" comp will most likely fail even tho you have way more %. Lets say for example a team that has 3ple crown playing 442 and now is 65% with same formation and comp than last season and yours its 3ple crowned as well but since you have 90% you go for a new formation, trying substitutes and stuff on to this match. There is a chance that you actually might lose this game.

Edit: there are also counterformations and other counters such as bonuses ingame, def against attack..etc