Host support for Instrument plugins in VST3

I’m implementing a host for VST3 plugins and so far I’ve got the Effect plugins to be working (following a similar path as the “editorHost” and “audioHost” which came with the v.3.6.13 SDK with a bunch of changes to make it compatible with the rest of the software and working without JACK client).

However, the “Instrument” plugins don’t generate any sounds, meaning that the output buffer I get after the process() call is a flat zero. What could potentially be missed (i.e. activating a state, setting a mode, setting up a bunch of calls, etc)? I’ve looked into the docs, but there is no clear indication of what’s specific for Instrument plugins for example.
Any suggestion about the possible modifications/calls to support Instrument plugins is really appreciated!