I had this problem with my 2015 XE and it turned out to be a software problem which was rectified in about 10 minutes by plugging in a Jaguar laptop and downloading a patch. Apparently this is a common problem but easily sorted.
Jaguar stopped selling isofix kit some time ago. Look on eBay that's where i got mine . They may be hard to find and pricey i payed £135 for them last year.
Hi just bought my first Jaguar at 72 years old a 2002 X Type 2.1 petrol auto with 89000 miles on the clock and it drives as sweet as a nut as they say. I have always wanted a jag going back to when i was a kid and all the films always had the crooks driving Mk 2s, so my dream was always a 3.8s cant afford one of those so hence the X Type.