So I've closed by boot lid / trunk and got into car and drove off.. Sometimes it will its open on the dash so I would go out and slam it and its closed then.. Other times I'd open it to get shopping out, and close it and go to lock the car but the car won't lock as the boot would seem closed and latched but it sometimes isn't' recognizing its closed and latched so not being able to lock the car.
Is this an issue for the latch itself and needs replacing or is there any adjustments to be made to make it "closed" so i can lock the car...

when i close it it generally does look and feel closed fully, it just doesn't seem to be recognizing it's closed fully.. either that or its not? I don't know.. it's just annoying sometimes

 

Here are a few simple and cheap things you might try:
Could the key fob button get inadvertently pressed or stuck? Take your spare for a few drives.
Maybe put a little lube in the latch mechanism and exercise the emergency key plus a little graphite.

 

I seem to remember on my car although a convertible the principal may be the same.
There is a plastic flap that covers the latching mechanism. This should move when the door/boot strikes it when closing and exposing the metal parts of the
lock.
This flap is held in place with lugs. The flap could jam and prevent the boot locking sometimes
I took the plastic trim off that covers that rear section of the boot and removed the mechanism. I seem to remember I super glued the lugs back in place.
I can’t remember the exact details but it’s been fine for quite a few years.

There must be a sensor on .
You don’t say whether it’s actually locking or just sensing it’s not locking

 

Jaguar latches are electromechanical devices. I haven't needed to disassemble a tailgate latch on the X150 but the dash message will almost certainly be triggered by a microswitch in the latch. Provided the tailgate is actually CLOSED and the only issue is the WARNING message, I think you need to repair or replace the latch. Such an invalid message will also inhibit locking.

Graham

 

I once had a real problem with the boot not locking. It turned out to be THERE WAS ANOTHER KEY IN THE CAR that I didn't know about. Weird, but that's what it was. I had even taken the car to the dealer and they couldn't figure it out either. I found the key like a week later. I also believe I blamed my grandson for losing that key earlier so I bought another one.

 

I solved the issue. it didn't seem to be latching fully. So I opened the lid up, removed the bottom part of plastic cover to get to the bit the latch latches on and unscrewed the 2 bolts either side of the "hook" bit which the latch "hooks" to.
upon loosening, it gave some up and down play.. so i pulled it up, and tightened the 2 bolts either side. Put everything back together and it closes, latches, and now locks with complete ease now.

Very simple job.