Well, it might be because you did not synchronized the progress already (you might have clicked on SKIP when the synchronization was in progress).. And you local storage limit got over.... In that condition ... Read the section 1 : Setting Local storage to unlimited
This will not make your progress come back but prevent this case in future.
If you skipped synchronization, then it has not been synchronized and saved. You have to put the storage to unlimited. Unlimited, because PB2 doesn't really use much bytes.