Download my Whole Lotta Stratis mission from STEAMWORK, save the game anytime when playing it. E.g. already after start dialog. Exit to game menu and try to resume the mission.
Identical version of the mission can be downloaded from here to play it old way (pbo in missions folder -> start in scenarious), with this resuming works without problems and its the same versio of the mission (only created to missions folder in editor):
https://www.dropbox.com/s/bzuljnqrxgqvg5c/SPWholeLottaStratis.7z