Likely worn hinge pins. Very common and not much you can do about it in my experience, although other suggestions of trying a rubber spacer under the roof side of the plate may help a little. The looser the hinge, the faster the wire harness fails. Last time I needed one I was able to get one from a yard that was still in reasonably good shape, albeit slightly pitted with a broken ground wire. For whatever reason I had one side more worn than the other. As long as one side has a good ground wire you'll be okay, or you can attempt mending the ground.

Surprisingly, ipd appears to still have stock of both the original chrome and the later black anodized hinges (identical mountings), both left and right side. Even more surprising is the prices (you won't want to look).
https://www.ipdusa.com/Catalog/Index?searchwords=240%20tailgate%20hinge

There's the odd new one on eBay as well, but not much cheaper. Skandix (in Europe) shows a left side chrome one still in stock at an extremely reasonable price that would be well worth the shipping and duty, but the odds of it actually being in stock are probably slim. As the chrome ones are NLA from Volvo there's probably no point in placing a backorder. The black ones are still available in the Volvo parts chain.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

It's definitely bad hinges, I have 3 of these cars and they all have the same problem. The all black hinges warp and the pins inside wear the hole out so it sags down. They don't offer them new anymore either. I never had this issue with the old chrome hinges. And someone correct me if I'm wrong, but they are a different size than the chrome ones.

AFAIK, there isn't any adjustment.
This seems to be a common problem, maybe someone has come up with a solution?

The hinge on my previous 245 failed when I was on holiday in Austria. It turned out that a PO had mixed up bolts. This resulted in one of them just hanging on by a thread (literally) or two until they tore out when I closed the hatch.

I forced the hatch closed, leaving a gap at the top and went back to the camp site. A fellow camper kindly donated me a longer bolt to use all of the remaining thread.

A couple of years later I decided to buy and fit new hinges (along with the broken wiring through them) as it was hanging low, making impressions on the aluminium strip. Suffice to say that the new hinges did not change a thing.

I did not see any way of adjustment. Maybe you could stack some shims between body and hinge, but then the rubber won't seal anymore.

I decided to live with it.