I loaded several sets of images into Lightroom over the past few weeks, star rated them and processed the top files to JPEGs for uploading to my SmugMug account ..... been doing that for years. Just noticed that several sets from last week lost their star ratings ..... No change in process. The sets from this week and three weeks ago are fine. what to do???
1) How did the star ratings disappear?
One possibility, in Grid mode, entering a 0 (zero) will remove any star rating from a select image and if several or all images were selected when the 0 was entered, Stars would be removed from all selected images.
2) Possible solution?
Depending on how often you back-up the Catalog, you may be able to go back to a time before the Stars disappeared by opening an earlier Catalog from your backups.
No certainty, but a good guess.