I have now downloaded and installed Waves Central. No plugins were listed, but there was an option to uninstall V10 and V11 versions (generic selection - no actual plugin names - I can only assume that some time in the past I DID have some) so I ran that - which said it completed successfully.
Now Cubase gets as far as “Initializing: VST 2.x Plugin Manager” then quits silently after a few seconds…
I uninstalled and reinstalled Cubase Pro 10.5 to no effect. It got as far as checking VST 2.x plugins then quit without an error message.
I then renamed every VST2 plugin folder by adding “_OLD” to it - and Cubase loaded and ran.
Whilst my memory might be a bit hazy on whether I ever installed/tried a Waves plugin in the past - I DEFINITELY have not changed my plugins setup between 10.0.5 and 10.5. I realise that this error is dependent on what plugins a user has installed (all my plugins are 64bit btw), but am I the only one having the problem?
After removing all plugins from “C:\Program Files\Steinberg\VSTPlugins” and putting them back one by one, the issue is with “Groove Agent” (v4). I have no idea how to fix it - but at least Cubase now loads and runs.
It seems my version of Groove Agent 4 was out of date and needed updating from v126.96.36.199 to v188.8.131.522. A clue to the problem (via the software) would have been helpful rather than it shutting down at every launch without a message…