This bug isn't very important, but it's kind of hilarious.
I went to Kallisti Wharf to take some screenshots, because it's usually well-lit and has some nice scenery to pose in front of.
And I found this:
I had the same problem.
I eventually found Manticore. He was invisible, with just a slight aura visible.
And he was bouncing around a corner and didn't respond when clicked on.
https://youtu.be/7sYrF7ZpCD4
I had to log out, back in, and complete the mission from the contact.
This helped me quite a bit - I'm using a 1080ti on a Ryzen and none of the in-game graphics settings made much of a difference - even changing antialiasing from 32x to off didn't help. Reducing world detail from 200% to 100% got me a few frames, but going lower didn't help more.
This got me from ~38 fps up to 55-70. Which is still awfully low, but it's a whole heck of a lot better!