processBlock() not called

I've got a weird one.  A plugin in Logic where processBlock isn't called. Nor are any rendering/processing looking functions in AUBase.  

Other functions work fine, e.g. saveState. And the plugin works fine in other hosts.  Presumably something in the settings I'm returning which i'm about to go through in detail. 

Any obvious things to check? 

Fixed.  Needed some audio sending to it.  Unfortunate complication given that it could generate audio on its own as well :) 


Sorry if this is considered necroposting, however I am running into the same issue.
I am writing a VSTi and I am using SAVIHost (modified VSTHost) as a host for debugging. In Projucer I checked “Is a synth” and “wants MIDI input”, but processBlock still doesn’t get called, neither the float or double overload. Is this a known bug for the current version or is there something I have to do before seeing the method called?

It was a host issue in my case. If I didn’t actually route audio to the inputs the host didn’t call the plugin for any processing.

Indeed, switching from SAVIHost to VSTHost did the job, but I still think this is to be considered as some sort of a bug. If a VST is declared as a Synth, in my opinion it should not have to wait for incoming audio data. That is, unless it is host-specific whether the VST is called or not. The weird thing is, SAVIHost is specifically designed to be used to host VSTis alone.