Standalone and trouble with ConnectionProxy

Hi, I’ve been trying to realize a standalone wrapper of my VST3 plugin.
It’s a wrapper of processor+editor using PlugProvider, based on code from the samples.

I’m observing that some messages don’t reach the controller when they are sent from a background thread of the processor.

By searching a little deeper, I notice in ConnectionProxy

// TODO we should test if we are in UI main thread else postpone the message

Am I correct in assuming that this case is not yet supported?
How to fix it?