The grey lettering of Sublocation, City, etc. (white italics on Windows) indicates that LR has suggested these fields based on the GPS coordinates but that you haven't confirmed the suggestions. If the option Catalog Settings > Metadata > Export Address Suggestions is checked, then these suggested values will be included in exported pics.
The user-interface for handling these suggestions is poorly designed -- if you start typing in one field, the others get cleared. And there's no way to batch confirm all the fields in many pics at once. You have to click the label (e.g. "City") and then the suggested value, for each field in each pic.
Thanks for that!
I did have the Export Address Suggestions checked it seems, so thats all good.
So the only issue was replicating the data across the other pictures, I did this by using the Sync Metadata function which works well on blocks of photos, but I can imagine its a massive pain if you need to do it differently for a few different photos!
If anyone else has a good way to 'cement' these suggestions I'd love to hear them!
Please add your vote and opinion to this topic in the official Adobe feedback forum: Lightroom: improve control over reverse-geocoded Location metadata. That will make it more likely Adobe will prioritize a fix. No one in that thread has any great ideas for how to confirm the locations, unfortunately.