Lightroom 'forgetting' my edits

This happened to me years ago when I first got the new version of LR, then it went away and recently it's come back. With masking and the heal/clone tool, sometimes I will make edits to a picture then leave it for a while, and when I come back my most recent edits are gone and I see no way to recover them. Doesn't seem to happen with the main editing tools, and I don't see any particular circumstances that it is happening under... It has happened while the app was closed and also while I left it open. I've lost many hours of work this way and can't figure out what is happening!