Ditra matting is designed to protect your floor from lateral movement Natalie, (side to side) not deflection, (up and down)
So if the floor is bouncing it's unlikely the Ditra will afford much protection.
As far as stopping anything penetrating the
tile and grout, this too is unlikely.
If the Ditra is taped and jointed then it provides a waterproof membrane and vapour barrier below the finished floor surface.
I'd imagine that it's unlikely that it's taped because a kitchen is not generally treated as a wet area.
If there are no external signs of damage to the floor, try tapping the effected area with your knuckles, see if there is a change in sound to the surrounding tiles. This is not a definitive test of course, but can be a good indicator that there MAY be a problem below. It won't be a subtle change in noise but generally quite distinctively different.
But of course this would only be guess on my part, it would really need to be visually inspected, especially if there are no outward signs of damage.
If all appears to be in order and no tiles are starting to break free, then if it's not broke, why try to fix it, for now.
If the area appears to increase in size, then there's a chance the floor is starting to de bond from the Ditra.
But again, this is just supposition.
Sorry it's not much help, I'd just keep an eye on it for now.
And if you're going to have some kind of catastrophic failure, taking one or two tiles up and trying to repair the sub floor is not going to stop it.
Failures on that scale, will happen anyway.