I don't know what the exact problem is, but you can avoid all of this by setting the option to automatically save metadata to XMP
Thanks for the suggestion.
Do you mean writing the data to XMP sidecar files? I would love to have an option to automatically write my metadata to my DNG file, but would prefer to avoid sidecar files if at all possible, but if I can't fix the problem it is something I might have to consider.
Lightroom can automatically write metadata to XMP. For RAW photos, these are sidecar files. For DNG, the metadata is embedded into the DNG file.
Just tested this out and it does exactly what I want. Many Thanks
I have tested it on my catalogue and it embeds the metadata into DNG, PSD, JPG and TIF files, so I have no sidecar files and no longer have to worry about broken smart collections. Excellent news.