I've seen this happen when the citation hasn't been inserted into the current document directly, but has been copied from another document - especially if it's in a footnote. In that case the problem would be due to the referenced document not being included in the current document's reference list. Simply dragging it into the current document from the master list (assuming it's there) should solve that.
If that isn't the case, or doesn't resolve things, the next step would be to start Word in Safe Mode (hold down the Ctrl key while starting Word) and see if the reference updates correctly. If so, a rogue third-party addin is the most likely cause of the problem. Re-start Word and disable all third-party addins, re-starting each one in turn and testing until you find which one causes the problem. Disable that one and either delete or replace it.
Failing that, try repairing the Office installation (via Word Options|Resources|Diagnose).
The registry 'fix' you refer to amounts to invalidating two Word-related keys - the Data key and the Options key, so as to force Word to recreate them next time it starts. Deleting the Data key does resolve some problems; I'm unaware of anything being solved by messing with the Options key.
One final thing you might try is to close Word, delete Word's 'BuildingBlocks.dotx' file, then re-starting Word. See
https://www.msofficeforums.com/word/...locations.html for location specifics.