I was playing then I made that comment and left to go do other stuff. Now I log in and my save data is gone again.
The last update was about 20 hours ago, so I don't think that one was because of an update. Some people never have issues with the saving on the web version. Some people are constantly having issues with the saving on the web version. I don't think this is an issue I can reliably fix until Cloud Saving is the main saving method. The only thing I can suggest is downloading the game, as that won't have any save issues.