So my running theory so far: Agnes is the FBI informant/WITSEC. She's not just any old witness, she's an actual witch (maybe another of the Sanctorum's sorcerers gone rogue) and the amnesia hex/spell is her doing. The giant hexagon is literally her spell; a massive hexagram akin to one of those geometric shapes that we always see sorcerers conjure. I'm not sure if this was part of an intentional attempt on her part to capture and/or control Wanda (let alone her motivations) or whether this whole thing is just a confluence of unforeseen consequences (bit too much of a coincidence for my taste.) Regardless; even Wanda's subconscious was too powerful and volatile for her to get a handle on and she became just as trapped as everyone. The sitcom, the puppeteering people, the bending of reality is all Wanda. At first it may just have been her mind trying to protect itself from the combination of a magical amnesia spell and a grief induced psychotic break, but as the days have gone on she's become more aware of her agency, beginning to act out the fantasy until she's fully in control, starting with the "stop it!" incident and ending with the birth of the twins. I think Agnes is able to break character precisely because she knows what's going on and is cooperating with Wanda's "script", in the same way the 80's tech drone was able to retain it's form because it wasn't conflicting with the "production design".