I dont really see a problem there. Even in the manga adaptation its also the same (chapter 14 is the exact scene for the opening scene in the anime). They cant see spiritual beings but they know connie's actions, mannerisms etc are from scarlet that they always remind them. The only exception here is Randolph Ulster since that man can't be read and he's keen to see what's happening on his surroundings.
- Nvm6 months ago1

It's not about seeing any spiritual beings, it's about Constance standing 1m away from someone and constantly turning as if she saw someone. Scarlet presents is undetectable to others I assume, at least for now, but Constance action and how she behave is something that others seem to ignore. Her behaviour is far from normal natural reactions
- TerumiTenjou6 months ago

Randolph aside, no one mentions it because they don't know. To you, it is really easy because you see both, but to other people it isn't. That said the narration and even the same author mentions it because there are moments where Connie simply cannot act. That was the point of that moment where the Violet group lady tells Connie to face her. So yeah, you can excuse it to this anime adaptation being really bad.
