You haven't lost any cadence data. The cadence graph is screwed up, and it is that way for everyone. I'm fairly sure it is safe to assume it will be fixed sometime soon. You don't need to upload your activities again. The data is there, it just isn't being displayed.
If you want to manually upload your activities, you can do so here. When prompted for the file to upload, you may have to navigate to the .FIT file stored on your Edge 500 or, if you are using the ANT Agent, browse to the copy of the file on your computer.