Apologies, Danworld! OmniFocus stores individual changes in 'transaction files' which make up a timeline of the things that your copies of the app have done to your database.
It's possible that some sort of file corruption or disk error interrupted that timeline, causing it to look like things rolled back to the last transaction that happened before the corrupt one.
When that happens, the other transactions usually still exist on the disk; OmniFocus just doesn't know how to connect them up with the ones it is able to show you.
We work very hard to make OmniFocus reliable, but corrupt files can still happen and will affect OmniFocus just like any other app that needs to write information to your computer.
In any case, if you call us at 800.315.6664 or send email to
urgent@omnigroup.com, we'll do everything we can to get you back up and running. (Quite often, we're able to reconnect those transactions to the rest of your database, but it's something we have to do by hand.)