To Cor, that hesitation meant he'd be in the room for certain.

Finally, Cor did look away, but only slightly down as he thought how to word his next statement. After a long pause, he decided on, "Without going into detail, it's very likely what occurred, from what I saw of both of you." The marks on them both. The bruising on Ignis' neck and Gladio's cheek. The blood on Ignis and on Gladio and where it was.

It very well might mean he would need to stay in the same room as Ignis until he was certain that those missing memories didn't crop up in the younger man's nightmares.