It's a clusterfuck because prior to Abyssal Station Zero, quests establish a pattern: you are told where to go and you go there, and maybe you have to explore around in that area, but the answers lie in that area. But Clusterfuck Station Zero, the answers lie all over the DLC map, and there is no clear thing tying them together. So as best as I can tell, you are just supposed to explore around the entire map, until you find the submarine in Northeast, coodinates in another map, etc. This is not good design by any means. And I say this as someone who likes Underrail quite a bit as a whole. But this quest is not designed well. I wasted a lot of time fighting through those nasty Fetid Marsh areas around L2, thinking there is a hidden entrance there, but that was a complete waste, and 20,000 locusts died for nothing.
Expedition tells you where to go at every step.
You start and Aegis tell you to go to the mutie island.
You check the mutie island and report back and the computer tells you where Crimson Meadow/Nexus of Technology are.
You check those and they tell you where the hospital/security HQ are.
You check security HQ and it tells you where Blistering Shores/Abyssal Station Zero are.
You check those and you're done.
You get told where your next objective is every single time. The only way you can have problems is if you go to the security HQ before the hospital, or LemCo before Blistering Shores, but in those cases you should notice you can't do anything pretty quickly and go check the other area you were told about.
I dislike a lot of Expedition's design but it's not hard to find where you're meant to be going.