Why is it deleting?

I keep returning to spreadsheets to find that all the data (both newly entered hours ago as well as data that has been there for YEARS) has been deleted. The sheets are still there, but there is literally no data.

Any idea why this keeps happening? Never happened when I used openoffice.

Please indicate your operating system, LO version, and the file format you are using (ODS, XLS, XLSX), as well as whether the files have been edited by applications other than LO.