Okay so I moved the thread to the workshop, because the release board should be only for releases threads, not troubleshooting.
Now to explain what's going on, this is the secondary objective condition.
The primary goal must be done, Destroyed-ships must be 0, and Alpha 1 must have departed.
The reason the objective never fulfills all the way in the mission is because Alpha 1 (you) haven't left the mission. So it will appear to be incomplete for the entire mission. So that's what's going on there.
Now for the debriefing music... I haven't reproduced the issue exactly, but one of those conditions in the secondary objective are not true at the end of the mission. Alpha 1 has departed will evaluate to true in a debrief so that's not the issue. The primary goal sounds like its working properly too. So I can only think some ship is being destroyed and destroyed-ships isn't at 0 where it should be.
Try the attached mission, the secondary objective condition is a lot more straight forward. It's now just tracking all other friendly ships to see if they depart. If they all leave and survive, it will complete. If one gets destroyed, it will fail. Let me know if it fixes the issue.
[attachment eaten by a Shivan]