Is there a reason that in the VST3PluginWindow resizeToFit is only called for the Mac?
#if JUCE_MAC resizeToFit(); #endif
This is causing problems for us as it means editors can’t report their size until they’ve been fully added and made visible to a window (and peer).
What we’re seeing is that we ask the AudioProcessorEditor for its size, which is minimal, then try and set that, which gets constrained by the plugin and we end up setting it to its minimum size.
Changing the above to
#if JUCE_MAC || JUCE_WINDOWS works for me.