I found getting closer before disembarking helped. Strange.

Yes, as far as i can tell this only occures if you halt the Truck immediately when Adams tells you to. Moving somewhat closer, the game progresses as expectet. Maybe a somewhat too small trigger area?

Thanks for the report! A condition was firing too soon if you disembarked early, thus he would not move anywhere. This should be fixed as of today's dev branch update.

Mass closing resolved issues not updated since November.