I'm getting towards that (overall 97%, New LA and Primordia are 100%). Some of the segments left are annoying as it is tyrants I have no info on (so could be time or weather based, I think I've exhausted the basic mission board for tyrants too which has been a huge help) and I even have some normal missions in Sylvalim.
I also have one chest in Oblivia that I have no clue how to reach. It sort of appears on the minimap while in the segment but I can't figure out how to reach it almost seems like it is inside the rocks .
Usually you can get the info for weather based tyrants at the different camps on each map. Some are almost impossible to see without those tips.
For your issue in Oblivia, if it's the one SW of FN306 you have to fly very low in the abyss to see it. If not it's probably one in a cave and the entrance is often near but might be tricky.
Has anyone found a fourth halo?
I have 3 and I think they all come from normal quests like the wings and horns. I tried refreshing the basic mission board and none showed as reward.