maybe the HQ unit is the key. I tried my trick on a second planet so (obviously) Steve is correct about the Active button having nothing to do with it. Didn't have those units organized under an HQ
I guess having an HQ unit be required to do work makes sense, since my "HQ" unit isn't watching over me and I am looking through Aurora forums instead of working myself
I think I had ground constructors on the planet, then added a HQ, but they still didn't start building. I can't remember if I had the minerals in place before or after I tried to start the building (probably after I started the building, I probably kicked off the construction first to see how many minerals I would need), but I did move minerals to the site.
I was noodling around in the Ground Units tab to see if there was anything else I could try, I thought the Active button was the magic bullet (made sense to me) but maybe I just shook something loose.
Either way, turns out they worked for about 12 months and stopped and I can't get them to start again. . . must be on strike for better working conditions.