One thing that will impede even closing is if your struts are not a matched pair. I don;t know how many times someone had had a great Classic in the shop and it is so undignified to have to slam the hatch because one strut is new and the other is worn so the new side is fighting being closed and the worn strut doesn't offer much resistance.
Take look at the white labeling on the outter tubes. If they are not a matched pair one is most likely fighting the other. No need for LR genuine aftermarket works just fine. I have been fitting strong arm 4647s to later Classics for a couple years and never had an issue. They can be had online for easily around $35 for the pair. I used to fit URO MXC7833 that can be had for around $25 for the pair, but the Strong Arm give about 1.5" more lift.
I don’t think the design of the tailgate latches helps with this. I find that if I try to close the tailgate by holding onto the handle then one side inevitably doesn’t close. If I place my hands on either side and close it that way, then with equal pressure being applied it closes fine. I just accept it as being one of the quirks of RRC ownership.