Prime Missions are cursed, I'm convinced of that. With Season 4, I had 5 or 6 lined up, and then had the authors bail or disappear on me, and just in general had problems getting authors to bite on them for some reason. By that point the season was almost over, SR5 was looming, so we shelved it till Season 5.
We have the first Prime Mission in final production now. It's in final approval, layout, and art. Steven A. Tinner, GM to the Stars, was contracted to write the second Prime Mission, but sadly passed away last month. I have another writer lined up to fill that gap.
My own personal health issues kinda sidelined everything for a while as well, so that didn't help matters.
So Prime Missions are the bane of my existance. I'm determined to get that line rolling at some point though.