I have almost complete a full Galactic War when I finally came upon a sub-commander. I was like wow that's rare I haven't seen you guys since like update 67 somethin. So I go ahead and equip him on my tech bar and launch my next battle. Unfortunately I come to find out after landing on planet all the sub-commander will do is build one single Mex and then stop. He no longer completes any more buildings and does not move in the slightest. So i figure maybe its just a glitch so I brought him along on a another mission to try again, once again same process he does the same thing. So I've come to report a bug about sub-commander within the galactic war single-player not really working all that well.
Little update on this bug I had an old galactic war save from a previous build that which I'm not sure of the version number but none the less I had a sub-commander on its tech tree as well so I decided to give that a try. Turns out that, that sub-commander is fully functional. Now for the one thing that i noticed was that this sub-commander wasn't the same team color as I was. He was white and I was purple. I hope this help in solving the current issue.
I started a new GW recently (in the last few days) with the General Commander loadout (start with 2 sub-commanders), and they work fine. Maybe a little too well... there's often nothing for me to do while they kill the opponent. What faction are you playing as, by the way?
Yeah for some reason that one didn't work cause a made new Galactic war and got sub commander again and it worked go figure. So I guess its a once in a while bug.