Just a follow up to close this out, I removed the top portion of the controller and pushed the wiress in tighter through the feed area into the connectors. I replaced the top portion and, sure enough, the unit started controlling the sprinklers again. So after a year plus of running, the unit had vibrated (mounted on a garage wall near the door) itself loose. Reseating it did the trick.
So this brings me to my next point, the power test via a multimeter as suggested won’t actually be a test that can be conducted. This is due to the fact that the power supply feeds the top unit, which is why I was still getting positive confirmation that my schedules were running despite the unit not actually sending power down the lines.