Thanks for that Andy. I checked the file content, and as far as I can see syntax all looks fine, nothing odd stands out.
On that basis could there still be value in forcing that XML to recreate? I ask as I honestly don't know what that may or may not trigger to assist the issue.
I've done the same approach once more on a full flight, and same issue, and that was after deactivating some Community addons, it was worth a try.
Now, interestingly, and purely by chance, I just decided to do some housekeeping on another drive I use for videos, and came across the same approach from a few months back, and aside from some performance issues as I was probably still tinkering with sim settings, those buildings are fine!
Now I know the next sim update is pending, and I wonder if that may somehow fix things, but I'm wondering what may have changed in my sim, apart from a few addons (incl OMDB City Pack) and sim updates. Very odd.