i dont know its quite simple really every time you join you normally join resistance (to my knowledge) but you normally are on a team with way more people or your team has way less.
for example id say 70% of the games i join ill end up on the side with 6 people, the other team has 2. (this only happens on advanced big teams and standard mode) i really wish there where a fix for this to stop a team from dominating matches. 
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