Stuck at 98% completion. Can't find new quests.

The forward station south of the outpost. Fast travel to it and to the right-ish you'll see a tall red mushroom tree thing. Follow the dirt road up a hill and you'll see her barricade at the bottom once you round a slight corner coming down.

In the prima guide there are 200 secondary ops listed if that helps any. That incudes Allies, Additional tasks and Heleus assignments that become listed in completed missions.

OP is referring to the overall game completion, which is displayed in the save/load menu.

I was going for 100% in my second playthrough and gave up. I may shoot for a 100% again in my third playthrough, but its so frustrating.

I used the guide to help with some of the tasks but really the issue is the randomness of things showing up at each camp you visit. Things spawned better after I left and came back to the planet, but I get wanting to just get everything done in one go. That's not likely to happen with a lot of this type of quest.

As for the hidden caches, I don't think they would count toward completion since they are only there via an optional perk/cryo pod selection. The one you mention, it doesn't have the interact showing but if you hit the key (for me it's E with kb/m) you can get the loot in the box anyway. I found that out by accident, but it worked in my second game as well.

This thread smells necrotic... 

I used to check the task journal, but when it turned out that some quests are hopelessly bugged and will never be fixed makes that pretty meaningless. 

I remember that many side missions are missable in Mass Effect Andromeda.
There is an additional task where you got to craft a weapon on Kadara  for a woman under very limited time. Also i was noticed that Nomad Shield Crafting is doable but still remained under my undone missions.  :-)
It is not impossible to complete 100% on every map but i remember that before the latest official fixes one of the missions on Elaaden was completely broken and doing 100% on that planet was impossible at time. Later on this was fixed among many other missions.
Also few optional quests are missable in both Kett Bases on Voeld and Eos.

That's something that actively irritated me about MEA.  Too many quests or stories needed or implied you should have Jaal around, and my god he is boring and lame.