So, I just tried to reproduce the problem, and I can’t.
- Checked out clean repo of newest JUCE 4.2 tip
- Compiled the plugin demo (AU target only)
- Loads in Logic Pro X and also in Ableton Live 9 without problems!
I noticed that in Ableton you need to make sure AU plugins are enabled in the prefs, click “Re-scan”, and then also wait a minute or so until it actually shows up in the list.
About the Rez stuff: yes, the juce_AU_Resources.r file is not there anymore. And yes, afaik Carbon hosts are not supported anymore. But are there actually really any of them left??? (if so, which ones?) Live 9 is not a Carbon host (and it works fine there), neither is Logic. Cubase doesn’t support AU in the first place.