Hi,
I use MIR Pro 24 as a plugin in Cubase 8 (currently in trial license). Every once in a while, MIR Pro loads (and works just fine) without showing the interace window. It doesn't appear in Mission Control, and can't be raised by clicking the corresponding button in the plugin interface. Alt-Tab or other methods of switching don't work either. It also doesn't help to select "View > Instruments" in the menu.
The only way I found of showing the application window is by opening the Preferences window. When it appears, the application window opens up immediately underneath it, and it's then possible to click cancel and work normally.
This doesn't resolve the Alt-Tab issue which is still ineffective until the app is relaunched (i.e. after the above fix the application window appears in Mission Control but Alt-Tab has no effect except for changing the front app in the menu bar).
Also, when this happens, you sometimes can't bring up the MIRx Settings Window, or when you do, you can't close it again (clicking the red close button just highlights it).
I can't reproduce this reliably because I don't know what's causing it, but it happens enough times that I would remark on it...
Best regards.