are you referring to this? =>
http://www.sonataserver.com/??
What you could do is look at your auto import setting in directly in JR16 (not this sonata thing) and make sure all the paths are included to the music which has disappeared.
Difficult to help you, as this is a apparently a third party application which could even be a server too ... not sure when it has been updated and frankly never heard of it. Looking at the site for 10 minutes though looks like everything it does can be done within JRiver -- its just an advanced setup with multiple custom fields and views, using dbpoweramp's metadata subscriptions?.
If Sonata is no longer supported, you might just want to spend the time and learn JRiver, its pretty easy to add the metadata fields you currently use).
If not, the suggestion was not meant to be unhelpful! JRiver 16 is OLD. You can install version 20 on a trial basis (free for 20-30 days I forget)
without uninstalling your current set-up.
Then,
maybe, someone could help you. I doubt anybody even has version 16 on their systems anymore Also, as this Sonata running on top of JRiver apparently, issues probably stem from that config and not the configuration of JRiver .. so you probably should be asking them. Or change the title of the post to "Any Sonata users here that could help me?" or something like that. Maybe Computer Audiophile site could be a source, google that .... there is a post or two.