Soft Lock on Trial of Corruption

I'm am in the second run of act 2 and have assembled the horn. The quest marker says I need to use the desert map to go to the Gates of Halani to clear the sand storm. However I have no travel point that allows me to go there.

When I use a waypoint to go to the gates I have to replay the mission where we initially open the gates.

So at this point I cannot progress to the last part of act 2. I also have the horn of vastiri stuck in my inventory.

Has anyone seen this or have any ideas to get past it?

Just go to the front of the caravan, there should be a marker where you can blow in the horn. When I first played I got confused too, because there is no useful description of what to do