Where is the adra arch in Sagani “The Long Hunt” Part 2

The correct order is

Right, Middle, Left, Right

Alternately, you can find a key in the same room where you found the clue that allows you to bypass the whole thing.

This seems to be a known issue that may be patched in the future, according to a dev on the obsidian forums:

We currently darken areas of the map that are beyond the line of sight of your characters. I do agree though that the inconvenience not being able to see the map clearly far out weights the value of line of sight radius information. I'll bring this up and see if we can fix in patch.