Here’s something I noticed with (64 bit) Pro 8.5.15 update on Windows 10 64 bit:

During the Cubase Pro 8.5 splash-screen initialization if the VST plugins manager initialization routine encounters a plugin for which the DEMO period has expired and that plugin generates its own popup warning of the Demo period expiry…
Cubase does NOT allow the popup to be displayed on Windows 10 and the Initialization routine appears to hang indefinitely.

to display the popup you must press ALT-TAB.

HOWEVER… even though the ALT-TAB will display the popup you cannot bring the popup into focus and dismiss it.
You MUST either terminate the Cubase Pro application with the Windows 10 Task Manager or Restart Windows entirely.

Working and tested example is with the expired Demo of VST LiquidSonics REVERBERATE v2

see attached screen capture of the ALT-TAB press:
The workaround solution is to uninstall the offending VST Plugin, however this problem could result in unnecessary end-user stress. It would be a good Idea to correct this behavior in future updates to allow the initialization routine to pause for the popup.