Wonder what actually is the cause of the target switch? There are rare times where the wrong target type spawns as well on Gold. Like a pyro target will be the first target when it was supposed to be a Prime.
I speculate it's the order in which the units spawn. Let me elaborate.
How fast the units spawn literally seems to depend on how capable (possibly tied to FPS rate as well) the machine running the game is. When I watched some console gameplay videos and when my FPS tanked, spawns seemed to take like 3+ seconds to spawn all the units, while at other times, when I was playing on higher FPS, it seemed to go much faster, which brings me to the main point, which is that these units were spawning slowly, bigger and more costly units usually spawned the last.
I may very well be grasping at straws here and pulling stuff outta my ass though, because I have next to no evidence except my memory.
edit: it also doesn't explain why target switch is so rare on Platinum.