I am encountering this also. Trying to finish Lightfall but Desparate Measures will not start. I tried skipping the lead in as Esoterick did but no luck. Went back to see if it worked by doing the concourse work but they never die either. I am going to shut down and unplug to reset cache in case the whole mission is cached and did not like my first go around (even though Esoterick did it). Will report.