I spent the whole day thinking in the background what could have happened…
One idea: did you by chance declare your own magicState instance in your AudioProcessor?
Since the introduction of foleys::MagicProcessor it comes with it’s own instance of
MagicProcessorState magicState;
If you have your own magicState declared in your sub class, it will shadow the protected magicState from the super class, and the MagicProcessorEditor will not see your oscilloscope, and the other issue that editing classes has no effect could also be related.
Can you please verify that you didn’t add your own MagicProcessorState?