I face a similar issue with Halion 5. In the list of instruments, I see an instrument that I had installed in Trial. Before the trial license expired, I uninstalled the instrument using Windows’ Add/Remove Programs. It was removed from the list of instruments in Cubase but it is still in the list of instruments in Halion 5. If I select it, the Cubase freezes with a warning about the license.
UPDATE: I managed to remove the instrument using Windows Explorer: I searched for all files containing key words from the name of the instrument (I searched for “Hypnotic”, for the “Hypnotic Dance” instrument), then I removed the relevant files. Cubase needs to be closed, for the files to be unlocked for deletion by Windows.