When you complete all objectives and have to join the LZ with your squad.
The Ai leader stop his move and take his binoculars too often(6-7 time for 300m).

So the chopper leave your squad alone as you take to many time to reach the LZ, resulting in a "mission failed".

Uploading a screenshot of the problem, you see all our squad in the chopper (but too late) and the squad leader is making dumb thing with his binoculars. {F22237}