I have my photos on a NAS and have two mac's with (of course) two catalogs which I synchronize after I edit something on one of these computers.
I edited the metadata on one computer and saved this to file (on the NAS). No alerts remain on this catalog.
Going over to the other computer I synchronized the folders, selected all the files that had any metadata alert and chose to update them from the file. So the metadata was (confirmed) read from file.
However the following alert remains on some of the photos even after removing and re-importing the folder :
Metadata File Needs To Be Updated
For this catalog it would be no problem to just write back to file since all the metadata is correct, but than the other computer/catalog would be showing an alert that something has changed and needs to be uploaded from file.
So, that would just be chasing my own tail, going in circles.