Generally, you should run DISM first, then SFC, as one is supposed to follow the other.
If it's not too much trouble to restore, I'd say make sure contents of C:\Windows\SoftwareDistribution has been deleted and give it another try. If that's a hassle, no shame in pausing updates and waiting...
Wow, that's wild. Good thing you had a backup.
I'd try running DISM and SFC on your current install to verify there's no problems:
DISM.exe /Online /Cleanup-image /Restorehealth
sfc /scannow
Then stop Windows Update services, delete contents of C:\Windows\SoftwareDistribution
Then try again.
Right, but Microsoft stated one of the major changes coming to Insiders is the ability to switch back and forth between Beta and Experimental without having to reinstall and losing apps and data. Just wondering if that has started yet.