Same problem for me.
After completing "Task: Herbal Entrepreneurs" I cannot give the "antibiotic plant" to the Turian refugee... I believe that particular task is "Task: Running a Fever" - which does not show up in my journal at all.
My order of operations was: Found the Nexus refugees, talked to everyone inside (got the UV light) and then completed "Task: Broken Family" by repairing the comm equipment. I did the anti-AI hackers (Knight) next, then left the planet to craft the item for that. Returned, went north and got the Outlaw SOS which led me to the stoners. Gave them the UV light, scanned the plants (no option to pick any up). No further Tasks started, and I was unable to give the plant to the refugees.
