On The Outlaws (Second Raynor campaign mission)
There are invisible walls. The first one is right above your marines as you start the mission. There is an invisible object blocking your exit from your base, and there is only a small hole on the left for them to go through. Again, it happens by the chain link fence right that triggers the hellions approaching warning, there is a wall with only an opening on the left side to go through.
I also found the same issue.
There’s an invisible wall in the starting base and at the fence that leads to the hellions.