After uninstalling C9.5 Pro (apparently there is no way to just roll back the update itself), reinstalling C9.5 Pro, and then updating it to 9.5.41, all of my plugins (including VST3) are functioning again. So, at least for me, the problem was clearly 9.5.50.
This must be Steinberg’s plan: release an update that breaks existing functionality so that when you reinstall your previous version you appreciate it more, despite its many flaws, becasue at least it’s better than the new version. Very clever.
I just switched from Windows 7 to 10 and recall being able to select the updates in Control Panel > Programs (what’s now called Programs and Features).
I would not consider it “solved” if your Pro version of CB 9.5.50 is not recognizing VST3 plugins. Now that you know the procedure to easily uninstall the update you should give it another shot. It is possible that the installer somehow missed the VST3 location.
Hey Prock, I actually did try installing 9.5.50 several times including from a complete reinstall of the full (~9GB) installer, deleting the entire settings folder, updating Windows 10, rebooting, etc. And for every attempt the same exact thing happened – Cubase failed to recognize all of my VST3 plugins.
Thus, I definitely do not consider this solved.
But no worries, I no longer start new projects in Cubase (I switched DAWs last year). At this point I just use Cubase to edit old projects that I didn’t convert over to my new DAW.