Why does launchd suddenly complain about error 78: Function Not Implemented? [long]

I have an old 2010 MBA which runs High Sierra. It is located at a condo which I visit for a few days each month. The machine runs 24/7 mostly to upload webcam photos to a host every four minutes, to assemble and upload a time-lapse video every 24 hours and to perform routine maintenance tasks. Here is the webcam page: Cha Am Cam

All of this is done with bash shell scripts that are run via launchd with the help of Lingon.

When I arrived...

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