I too had to drill the two carbon Duct mounting bolts & helicoil the holes to accept new original size torqx bolts.
It's the bit of the bolt that sticks thro' I found was the problem. One did actually turn 1/4 turn before it locked up, retightened it then cleaned & wd40'd the protruding bit of the bolt.

I now have a 2020 MY SVR and after a few days of purchase checked the car over.. to my horror I found the carbon ducts missing.. now not wishing to allege that the supplying dealer (it was second hand) had had them away I tactfully rang the dealer to see if my carbon ducts were still laying in the workshop post service…
I was reliably informed that JLR now delete the fitment of carbon ducts on the later cars… the callipers still have the mounting holes for them and this area is still unpainted but presumably there were just too many warranty claims for new callipers to justify their continued use… gutted as they are exquisite!

Wow....mines 2016.... thought to aid the cooling they were a must ♨️ What With the position of the intercoolers each side restricting straight thro' flow & more importantly keeping the V8 cool. 😎

Land Rover on a cost cutting exercise maybe 🤷‍♂️