This is strange behavior. Did you test it locally? Upgrading to a new version should not delete data. Overview pages are just a visualization of the data. Maybe this is a different issue?
Stop the upgrade and do not deploy it to Production, before you have a successful upgrade. But you already got that part, I guess.
To find out what went wrong, start over and do a clean upgrade without any other changes. Check the database itself, not just the overviewpage, because it might just be one single field that got renamed, which wrecks the retrieve, for instance. Losing the data can occur at changing attribute's datatypes, or at moving or renaming a constant. And some other reasons.
It might also be a solution to restore a backup after you have finished the upgrade.