I tried Hyde Food from The Bentley dealer, not good...It did ok on the seats but it started to remove the "paint" from the leather on the dash roll, and on the seat backs, nothing ghastly, no one but me would notice...that stuff scares me and I never used it again, Here in the states I got a leather cleaner/conditioner from "the chemical Guys" (website) and it seems to do a good job without causing damage.
The current product is named Connolly Hide Care because some idiot somewhere apparently thought that "Food" might mislead someone.
What you describe is not limited to Hide Care. As you've described, Connolly leather is not dyed in the conventional sense of the word (vat dyed leather is) but has a layer of "leather paint" applied on top of "leather-colored" leather. There is no effort to dye since the paint is opaque.
Like all paint, and particularly paint exposed to the conditions of the interior of a car and the high temperatures they can reach in summer, it ages and chalks, sometimes in a way you can see and sometimes not. It is not at all unusual for the chalked layer to be removed by the first application of any number of leather conditioners because it's nothing more than a form of "dirt" at that point and will be lifted by cleaners and conditioners. You can see this process occurring naturally as Connollized leather wears and the painted dye layer becomes thinner where it gets the most physical contact or "slide over" contact. Many call it "patina," and I think that's a good way to look at it.
Even if you redye (repaint) the leather over time the same processes occur, though you can slow them down if you're religious about conditioning your leather.
One should not be shocked if the first application of leather conditioner, particularly to the more exposed (read: top roll and edges of seats constantly exposed to sunlight) results in some removal of color. This is even more likely for long neglected leather.