Why couldn’t Annie see through “Ashok’s” illusion. That’s literally her whole thing…Okay, as the spoilers are flooding the social media space, I'll answer this one.
Annie's illusion thing isn't always on, she needs to use it. If she's not expecting an illusion, she has no reason to check. All that said, this is also a scenario where if someone like Annie could see through it in the handful of times she saw Ashiok, "Ashiok" could have edited her memory of those events.