I told my friend what Jasper said, but she said “When they fuse, a split personality takes over and they don’t remember fusing, like a hangover. That’s why Peridot isn’t getting a response. She thinks Yellow Diamond is on Homeworld, but she isn’t.”
Except Ruby and Sapphire were completely aware when tehy split from garnet and garnet and pearl were completely aware when they became sardonyx so that theory won’t work.