It might be helpful to have a preview of the current profile synced to Anki web and the profile currently open when you sync your desktop to the online version.
I unknowingly had another profile open on Anki web than the one I was working on in the desktop app when I tried to sync them. This meant when I synced I accidentally saved over the profile I was working on. When I tried to load a backup, the backup had saved the change and I lost weeks of work.
I feel like this is an easy mistake to make, and quite a costly one at that.