Task: Herbal Entrepreneurs doesn't let me take a plant sample

I have a very similar issue.

I encountered the Nexus family house (The one where you pick up Task: Broken Family) on Kadara before I acquired and tracked down the, ahem, impaired individuals who sent the SOS in Task: Emergency S.O.S. So I talked to the salarian who gave me the UV lamp and the turian with the sick friend early on. After completing Task: Broken Family, I completed Task: Emergency S.O.S. (because I already had the UV lamp), but because I already had the UV lamp, the Task: Herbal Entrepreneurs never popped up in my journal (it wasn't given when I picked it up conceivably because I hadn't started Emergency S.O.S. at the time), so I am unable to collect the herb sample from the, ah, gentlemen in the S.O.S. task.

TL;DR: Basically, my issue is the same in that I cannot collect the herb sample. The underlying cause appears to be different, however, as an issue in plot flag order seems to have made it so that I don't have the quest in the first place. 

I suppose going back to an old save might fix it, but I completed the Broken Family task on a visit that occurred some time ago, and I'd rather not lose a quarter of my total progress for a single quest. 

(P.S.: OP, I think the "memory size in GB" is referring either to your RAM or VRAM; I don't think they make 500GB VRAM devices...yet... and if you have 500GB of RAM your system must be wild indeed)