[Edit: Solved - I had to reinstall ‘Steinberg Activation Manager’ and got Cubase UP and running.
Installing rest of the libraries. Yet to see if the original issue shows up, fingers crossed]
Original Problem: After upgrading to Cubase Pro from Cubase AI, Halion Sonic SE Artist Library didn’t load (all sounds had a Red Warning Symbol) and I ended up uninstalling Cubase. It was finally resolved after reinstallation.
Secondary Problem: Steinberg Activation Manager was stuck after reinstallation of Cubase. This was resolved by reinstalling Steinberg Activation Manager.