BLUF: achievement machine broke
This should be for finding all the montipora in one delusion (24), while sunk is for finding all the montipora in all four delusions.
There are a total of 63 montipora with 24 in each delusion. Now, I know that 24*4≠63. This is because the montipora depend on your decisions. Their location never change, but the dialog does. Up until the first choice, the montipora only give one dialog option each. After the first choice, the montipora each have two different dialogs depending on whether or not you trust ALTA. And of course after the second choice, each montipora has four different dialog options.
Unfortunately this achievement does not unlock as well as Sunk. I originally thought that it was because the game would randomly crash, or if I quit the game, but I even managed to find all 24 in one solid run.
Also, if anyone thinks I missed one, I did some snooping in the assembly for the Steam version and the requirements match up with 63. There is however an unreachable montipora in the first level, but I'm pretty sure it's just static or for testing because the numbers wouldn't add up if it was.
The devs are aware of the issue, but feel free to contact them, every little bit helps.