Random Songs is only getting tracks from a tiny subset of library

I've never seen this behavior before. I have a large library. Random Songs is only getting tracks from a tiny subset of them. It looks like just the most recent New Music is included. That's unclear because this past week I set up a new server and scanned in the whole library without the use of any previous databases.

It was fine till this morning, when this started happening. I looked at last night's rescan for new and changed files and it looks like it ran fine.

Any ideas?