I’ve spent a little more time. I can see what’s happening, but not why.
After entering a command, the modified generate action rule is invoked once with all variables zero (action, noun, second, etc); and then again with the real action value. This happens in both the debug and release versions.
In the debug version, 0 is the debug “GLKLIST” action. It doesn’t actually execute. I’m not sure why not. (It’s not that keep_silent is set, I checked that.) But it gets past the “check for missing noun” test, which of course it passes, because that action takes no nouns.
In the release version, 0 is the “GO” action. Since there is no noun, it fails the “check for missing noun” test, and you see the error message.
So your answer is, something is triggering an extra action execution with bad data. This bug exists in all versions of your game, but it happens to only print an error message in the release version.