If you have a clear cookie/cache option on exit in your browser that might be the cause of the issue.
Atm the save system is using the browsers local storage.
I do not have that option activated, as all other games that also use the local storage still hold my save...
Another thing I found out is, that when I duplicate the tab it gives me a fresh save. But if I first made a manual save it sometimes gives me the same as the save of the other tab....
But okay thanks for working on a save system with export/import ;)