I may be too hard on myself!
In any case, I have run into another problem:
It also gives me "error 2" sometimes.
The workflow in question is generated from an AppleScript that gets a selected number of Keyboard Maestro macros and adds them to a JSON script filter. The JSON seems to be valid (JSON Editor opens it without a problem, and it is more fussy than Alfred). I've tried `chmod +x`, launched from the AppleScript and from Terminal. Also, the script won't run from the Alfred script box this time (the window appears but nothing drops down). I've put the script side by side with others that are still working for me and I can't see any meaningful difference.
https://www.dropbox.com/s/zz55r42jvyejwv6/__Script Filter test.alfredworkflow?dl=0
FWIW, tried this on both Catalina and Monterey.
There's probably something very simple that I'm missing again. Trying not to be too hard on myself!