What does that mean? In the theory, it's a message for Eren from a dystopian future (yes, even more dystopian than current world) where humanity is about to extinct and key moment that leads to this catastrophe is the time when SnK events occures. Another evidence that support this theory is the dream of Eren.

Is there a loop in AoT?

The final chapter of Attack On Titan's manga landed earlier this year, but Isayama himself added some additional pages to the printed material as a part of a "Director's Cut," which definitely lent more credence to the idea that a time loop was currently in place.

Is Mikasa in a loop?

Relations. Mikasa is a member of The Heavies, a group within the Attack on Titan loop that strives to protect other loopers from the Titans.