Simple: if you're f2p, and the next attack would take out the AI's toon, then it becomes _very_ likely that the toon will dodge the attack.
I don't really know if this applies only to f2p, but I've seen this sequence of events happen _way_ too often to be just bad RNG. I've never had 15 consecutive dodges, but I have lost battles because I was about to take out a toon (often Sidious) and, near "death", he would dodge every single attack (at least 8 of them) while his mates quickly made short work of my team. It should be mentioned that the player does not have such a benefit of the "dodge of life" (at least, I usually don't); one more of those situations that make this game "fair".