The mission screen says to build a Colossus Geobay. I built one and got in the Colossus to make it the main exocraft. The mission details didn't update.

Check that particular mission is the one selected under the Log section of the escape menu. I've noticed that it is possible to "do" a mission but have it fail to register unless that is the active mission. I think you can just go to the Log section and select that one and have it accepted but that whole area seems to be a little shakey.

I've made the mission active and hopped into and out of the Colossus several times. I even deconstructed the Geobay and built a new one. No change.

I had this exact issue with the Nomad Geobay. Deconstruct the geobay & the exocraft terminal. Then rebuild the terminal and talk to the engineer who will once again ask you to build the geobay. Now build the geobay and it should work!

Updated to the latest installer and this mission progressed.

Turns out there was also another mission with the farmer since after turning in a harvest the quest line had just ended without making a new entry in the log.

Once I got back into the game I saw the notification to talk to both of them.