Dear Lazyweb, do you recognize the error "The output device Loopback Audio does not appear to be attached to your Mac"?
That device is indeed no longer listed in Audio Hijack or in system sound preferences.
This is a macOS 10.15.7 Mini that had been working fine until a couple days ago. I haven't intentionally made any changes recently so I don't know what melted. I tried re-downloading Loopback, re-installing ACE, upgrading to Audio Hijack 4.1.1, and rebooting. Same.
I mailed Rogue Amoeba support yesterday, who are usually good about these things, but they haven't responded yet and I'd really like to have this fixed before... 8pm.
Update: Fixed. Turns out there was a "turn it off and then on again" checkbox that I had bonked before rebooting that also wanted a bonk after.
the problem with virtual devices is that you can't just unplug and plug them in again.
Turns out there's a "turn it off and then on again" checkbox that I had bonked *before* rebooting that also wanted a bonk *after*.