The file was just a few-hundred kB and filled with just zeros. Other then using an old version (latest stable 4.10.2) there is nothing special about the configuration or workflow (file was saved to desktop; OS: Windows).
The problem seems to be similar to the one described in “Segments disappeared!”. Maybe there were some instability in how Slicer-4.10.2 saved segmentations. It may make sense to use a recent Slicer-4.11 version and create backups (instead of always just overwriting the previous version). If data corruption occurs then save logs of the last session (where the data was saved) using menu: Help / Report a bug.