This is typical of JSX snippets I run via KM. On OS X 10.13.6 (High Sierra) it works flawlessly in Adobe Illustrator 2015.3 or 2019. But in Mojave it works in neither.
This script is simply turning ON a Symbol instance named "test".
Ok, this may help. I turned on "Show results" and got this. I'll read some other posts. I'm sure the answer is here somewhere.
/var/folders/s4/kwh5wt4s7dj3kz_0q1cn6qq94kbk0q/T/Keyboard-Maestro-Script-BF1BC025-D6AA-4A80-AA23-4E20057B8139:48:81: execution error: Not authorized to send Apple events to Adobe Illustrator. (-1743)