Inconsistent number of botz in solo challenges

Is there any explanation as to why the number of botz keep changing for the solo challenges? For example, some matches say you have to play as many as four botz, but I've seen the number of botz between zero and four. The number of botz in a game like this would make a huge difference in your scores if the botz are good. A player could get a lucky game where there is only one bot (or even none at all). I would understand if some of the botz were lowered to make it a little easier for players to get a medal, but it should be the same number all the time, not up & down as I have seen recently.