Blank GUI on Cubase Pro 10 (VSTGUI)

Two customers reported us a problem with blank GUI (black rectangle, or minimized window) on Cubase 10 under Windows 10.
We are using VSTSDK/VSTGUI
Is this a known issue?

I don’t think so. Cubase ships with a few plug-ins build with VSTGUI. You can ask if they can open the “Step Filter” for example.