I recently edited a bunch of photos in Lightroom. A few days later, when I reopened the catalog, my smart previews looked normal and then suddenly reverted to how they were originally. When I clicked on "before and after" for the problem photos, the edits didn't save. I saw the smart preview revert in front of my eyes!
I tried updating my LR software to the most recent one to see if that fixed the bugs, but it still wasn't work. I exported the problem photos and don't retain any of my toning/retouching.
It sounds like you opened an older version of your catalog.
Check your File>Open Recent for additional catalogs you've opened recently. One of these may have your missing edits.
Yes to what Rikk said. You have a different catalog open then the previous time you made edits.
In preferences you will find this setting. It shows the path and name of the catalog you currently have open. If you click on it, you will get a list of all the other catalogs you have previously opened.
This button under catalog settings will take you to the catalog file on your hard drive.