I also use DXO PL5 Elite version and NIK Collection 5 latest version on a win 10 Pro laptop and desktop. I just checked the Metadata on a Tiff I recently made in Color Efex Pro from a NEF (raw) Nikon file. All of the MetaData and IPTC on the NEF appears in the Tiff with one exception. Next to the lens info (JPG) appears. In the original NEF file (RAW) appears. I think (TIFF) should appear and not JPG.
In some past version if NIK, more MetaData was removed. Going from memory it might have been time or date info. I do know that this has been an issue reported on before.