I don’t see how this is a new issue, scanning the code there hasn’t been that many changes to VST3 lately. But my users are complaining about it a lot recently.
If you call
releaseResources() on a VST3 it loses it’s MIDI input buses and there is no way to get them back. You should be able to call
releaseResources() when you aren’t using a plugin and then call
prepareToPlay() when you need it again.
setStateForAllMidiBuses (false); and the only thing that ever calls
setStateForAllMidiBuses (true); is
setupIO() which is called when the plugin is constructed.