Did you test calibre after the upgrade? It should have been just as it was under Win7 - well mine was.
Is calibre installed in the standard location i.e
Program Files if 64 bit,
Program Files (X86) if 32 bit?
I suggest you uninstall/reinstall latest calibre. You wont lose libraries or settings, but if you're anxious you could do this ==>>
How do I backup calibre?.
I that doesn't work then post a screenshot of
Windows Settings(Win+I)->System->About
BR