Hello! Before you say "You have to select a instrument or a preset", I have selected that but it still does not work. 1 thing I have noticed to make it work is to save the soundfont, and restart Polyphone. And also, after saving the soundfont and restarting Polyphone, even without selecting a instrument or a preset, the virtual keyboard DOES pop up. (There will be no sounds though because of not selecting a preset/instrument/sample)
This bug is annoying since, for example if you want to test your soundfont first without saving it and restarting Polyphone, it won't pop up or work.