It turns out there is a very likely chance one of the X-Men Red is a sleeper agent for a villain....

https://www.cbr.com/hunt-for-wolveri...sleeper-agent/

Now who would/could it be?

Jean just returned. Maybe she's not the real deal as we thought.

Trinary is a new discovered mutant, or not?

X23 and Tabby are clones, maybe it's them?

For each member there's probably a reason how they could be it. Though I find it difficult to see how it would be possible for Kurt, Remi or Ororo.

Let's assume CBR is right. Let's speculate.