In my ongoing effort to fix the small things that are at the level of my current mechanical ability, I found a cable between the ignition coil and the resistor(?) that definitely had seen better days.
Luckily my DS 21 is a July 1971 model, so it doesn’t seem to be plagued with the infamously bad wire insulations used a few years earlier.
While still functional, this wire was due for a replacement, so I soldered up a nice quality wire I had and made sure to clean, sand down, and tighten all the other connectors around the ignition coil while I was at it.
The jury is still out on if this fixed the intermittent ignition hiccups, though…