EDIT 9/9: added a video.
I get the “You dont have sufficient rank..” after a second or so when I try to create a mission whilst being in a different source of supply.
This happens to me frequently when trying to create any mission.

@mitchlin In your video you actually joined an existing players mission. That feedback on that screen should be updated to prevent confusion.
Have you tried using the new mission creation method? It’s that big “Green Button” to the left of “GO.” It’s actually quite easier and works properly.