i've seen this happen once and the problem was that the site had a bad hosting plan and caching and other factors made the editing flip out from time to time and somehow revert back in versions etc.

have you monitored the "Versions" list when this happens? Each edit save should generate a new version so if another save reverts everything, perhaps you can at least go back a version where everything is still there?

I've tried reverting back to old versions, but it never works. It just shows me an image of the version.