well, an option is to empty your sync folder (that one is not needed), then delete one or few of them and test the game each time, see when it works and doesn't to pinpoint the faulty save.
... actually, do empty the sync folder, then i suggest sorting your folder by last edit and deleting the one save that shows the most recent edit, that should be the one, as it then prevented you from making more or overwriting them (autosaves aside, don't consider those, i mean either a quick save or, more realistically, an actual manual save), try with that first, otherwise do attempts like i suggested above. If you delete every single save and it still happens, you are probably doing something wrong.
and don't worry for the deleted saves, they can be recovered from your bin with ease by right clicking on them and restoring.