TOPIC:

Exactly, you should have your foot on the brake to engage gear.

You can change from N into s gear but it’s common practice to ‘foot on brake’ from park through the gears, I wouldn’t think of selecting a gear without my foot on the brake unless I wanted a surprise!

Thank you for the advice on how to use an Automatic Gearbox.  Although I have held a full licence to drive manual cars since 1969 I have driven Autos for over 45 years!  As I have tried to explain.  it is NOTHING AT ALL TO DO WITH THE BRAKES (Automatic or Foot Brake )  but when reverse is engaged (after placing it in reverse BEFORE releasing the foot-brake)  NOTHING AT ALL HAPPENS for at least 2 / 3 seconds then and only then does the reverse drive engage with a jolt  As mentioned several times My brand new one made in June 2018 does not do it!

You’ve answered your own question, having two cars the same.

The dealer is telling you there’s nothing wrong with it, yet it reacts differently to the other vehicle.

Therefore the thresholds must be set different, the gear lever is just a switch, the gearbox ecu takes care of the clutch.

Whether you’ve been driving autos for years or not, the cars box isn’t a conventional auto box it’s a semi auto box with two clutches working alternative gears enabling faster changes, derived from the racing scene. The clutch is  managed by the ecu as well as the gear change, if it clunks in, its more like the clutch is not disengaged correctly, ie dragging

If the dealer disagrees try a different dealer or start a case with RUK.

Long story - short: It's actually a manual transmission, controlled electronically. The so called Robotised Transmission.
That's why, my guess was differences in software between the two cars.

The Kadjar auto is a Getrag dual cluch unit, the same or similar to what Ford calls the Powershift: