When using with Cubase Sointu displays the "VSTi host sample rate is 0hz; sointu supports 44100 Hz only" all the time.
The Cubase project is set to 44.1khz and everyting works as expected, except the error message overlaying the UI.

Suggests a Close button (X) on the error message to close it for this the current session, or simply not displaying the error if the reported frequency is 0 (as it's most likely something Cubase reports wrong to the VST api).