Since the event started I started with a map full of rivals and now I have all the clothes from the event I am rebuilding the region levels and trying to do so WITHOUT the rivals.
Remember that there is a 2 hour cool down between rival spawns in the same region. You can level up a rival if it is not already at level 4 but it takes 2 hours, about, for another rival to spawn in the same region. So after a rival has spawned, move to another region or grind the rival up in levels during those 2 hours. Rival spawns also have to do with points from destroying other machines, any other machines. The points go to rivals and the region and if the player is not to level 31, the player.
If all rivals in a region are level 4 then the region gets points and as soon as a rival spawns extra points goes to level up the new rival quickly. If you are building up a region, then destroy as many machines as possible in the 2 hours. I destroy any rivals that are not harvesters also as soon as they spawn.