Re: Voeld: Gone Dark, Catch and Release, Clearing the Air - NONE work.
I definitely ran into a point during the main questline when none of these would spawn anywhere, and the kett camps were entirely empty as well. Eventually it was fixed and I could finish them all and turn them in. (If you go through 3-4 camps and nothing turns up, you're probably in the same situation that I was.)
I believe the fix in my case was to progress with the main mission past a certain point. IIRC, I returned the Moshae to Aya, then finished A Trail of Hope and perhaps Hunting the Archon as well. It may have been taking HtA up through landing on Kadara, or it might have even been as late as retrieving the transponder on Kadara and speaking to Gil afterwards. Try progressing in stages and checking back to see if these tasks start spawning again.
Also don't despair if you run into a bug with an angaran bug (bad pun unavoidable). Several people, including myself, have found one angaran bug (in my case, the third one) unscannable despite chirping and despite SAM's instruction to scan it. Saving and reloading made it disappear for me, since they're randomly generated, but I found another one at the second camp that I crashed afterwards, where it scanned properly and continued the quest.
Good luck!