Hello, I’ve heard of this happening to a few other people as well. It seems to be a patching related issue as far as I know. How many in game days have passed since you patched your game? In the stories I’ve heard from other people it usually takes him about 5 days to show up again.
From what I’ve been able to glean there is something wrong where he thinks he is building something post patch, except since there is no building to construct he basically just disappears off the map. Once the non-existent building is finished he shows back up like normal.
Regardless, I plan to address this before the next patch. I’m currently pushing through controller support however so it may take a little while before a patch comes through. Probably sometime end of this week or next week. Hopefully, he shows back up for you on his own though.