I completed the feed Trudi side quest during my first playthrough. I have come back to Sargasso again and the quest is no longer working properly. I was able to pick it up but as soon as it gave me the objective it said that I have 60/15 of the Zurpstones. There are no Zurpstones on the map anymore as I collected them all the last time. Is there a way to trigger the guy to accept the fact that I have met the requirement?
I think you have to travel off-planet for a while and you will eventually get a call from Mort telling you that you have collected enough zurpstones to feed Trudi and you can return back to hand them into her. The same thing will happen again with the second part of the quest so you will have to keep killing time between the stages if you want to be able to get further with the quest.
You can check out the Help Trudi quest guide if you need further help with this quest if anyone reads this but did not collect all 60 of the zurpstones the first time around and is no playing on challenge mode.