I have a problem with version 10.0, the photo is of poor quality in the library and in the develop module. I use smart previews (the disk with the original photos is disconnected). smart previews in version 10.0 have poorer quality than in version 9.4 When I install the older version (9.4), the same photo with the same preset is of better quality (also smart previews).
It looks like there is a higher grain in the photo Here are photos exported from smart previews.
This has been confirmed by the team. Until a fix is issued your workaround is to disable the Smart Preview workflow. Preferences>Perfomance | Develop Uncheck 'Use Smart Previews instead of Originals for image editing'