So I just picked up this bounty from Xur today, May 9th; and it still has the Vex samples requirement on it. Though I have completed the original requirements of the bounty, those Vex samples are still keeping me from completing it. Do keep in mind, I have 2 more Xur bounties to do after this; with only 4 weeks till new dlc. Kinda getting worried.
The vex samples are still a requirement. Run the Warden of Nothing strike to get the samples.