It’s not just JLR.
When I got my Peugeot RCZ they charged £50 for diagnostic, which was knocked off the repair cost if you went ahead and got them to do the work.
Now they charge £75 which is not refundable, whatever you do. And that’s the discounted Price for me because I have a service contract with them, or because I have a Peugeot Platinum warranty, I can’t remember which 🥴 (I think the full price is @ £125).
Despite having all the above, every time it’s been in for a service, they always either suggest, or say it ’needs’ something that isn’t covered by either the service contract or the warranty. Funny that 🤔😐