I had exactly the same problem. During the playthrough of the oilfield campaign the bug was introduced and made it impossible to go further. Sometimes i managed by luck to get a mission forward in case there was only 1 external cargo but then the mission with 4 external cargos came and at least there it gets just a joke. 4,5 tons are lifted without any change in collective and swinging like you have loaded a popcorn on the rope.
The only possible way to get forward was to change to standalone, non-steam version and to roll back to an earlier version without the bug introduced in stable v