Black plugin screen in VST 3 test host GUI editor?

I have two separate but related questions.

I’m attempting to write a basic plugin as a proof of concept, so I built the sample plugin code created by the VST3 Project Generator, then loaded it into the VST 3 test host. All I saw was a black rectangle for the plugin dialog, but I assumed that was normal.

That is, until I opened the GUI editor and tried adding a slider control. Nothing appeared in the black screen, other than an outline showing where the slider was SUPPOSED to be. IS this normal? I’ve seen a lot of other people complain about black screens in their plugins under certain specific circumstances - but never with the VST3 test host.

Thinking that it might be a good idea to try the test plugin in a different host to see if it gave the same issue, I downloaded a trial copy of Steinberg WaveLab Pro 11, but I can’t find any way of opening plugins in the app. Worse, when I create an empty workspace and then go to File->Preferences->Plugins, nothing happens. No dialog opens at all. Is this normal for the trial version, or what’s going on?

I was finally able to get the plugin manager to open, after contacting support for help. Once I did, and once I opened a test WAV file, I tried applying the test plugin in the “playback and processing” window on the lower right. Clicking on the plugin did NOT display any dialog window AT ALL. When I chose another plugin (below the test plugin), clicking on that one DID display a dialog window. So I’m guessing that the ability of the test plugin code to display a GUI window might not be implemented correctly?