AU Lab midi mapping (host automation?) broken?

Or did it ever work? I just started trying to get a small setup with a single AU happening. I can play notes and assign midi CC #s to parameters in a plugin, but Command-clicking to open the midi mappings window does only that – I move a midi control as it directs but nothing happens. Notes no longer play and the application is "not responding." Clicking "cancel" in the midi mapping window results in a beachball and I have to force-quit. I've had zero luck with multiple google searches on a variety of terms, so I'm posting here. TIA for any help! I have the latest AU Lab (2.3, created March 6, 2020) on a fresh install of Mojave (10.14.6).

BTW - I am assuming, perhaps incorrectly, that "midi mapping" and host automation are the same thing. Maybe I need to be set straight there. I'm curious though – if Apple means this program to be a test bed for AUs that devs build, how could it not have some way to test host automation? This makes no sense to me.
AU Lab midi mapping (host automation?) broken?
 
 
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