I've been stuck on 11/15 side missions for no B's around 6 months. It's keeping me from a Platinum. I'm going nuts here. I try to follow the few guides I find but it seems like they were all written pre-prophecy and I don't know if they're even accurate anymore. I'll take any advice I can get, because this is seriously driving me nuts.
Edit: After months of messing around with this, I just started grinding Aethon system and all of a sudden got four side missions in the span of an hour. Apparently that's a great spot for them. Nurgle Infestations in particular game me the most luck, 2/3 Nurgle infestations I did in Aethon had a group of Guardsmen needing aid.