Got past this. Not sure exactly what fixed it, but I did entirely remove Cubase 10 and reinstall it (things were still broken), then removed and reinstalled LCC a third time.
Now I have issues with Cubase 10 crashing in ntdll.dll on certain projects. sigh
“Upgrade to Windows 10,” they said. “It’s more stable,” they said.
What you really should have done was a clean install of Win 10.
The upgrading Win 7-Win 10 has always been a hit or miss for some reason, but new win 10 install always worked.