Riggs Associates?

I just finished clearing all FG areas, except the challenge dungeon itself, and I’ve only managed to find 1 pack of 3. Spent a good chunk of time retracing everything twice, still can’t find another pack. Going by what the description for the achievement says, I’m guessing I can’t back out and load the world again, so am I just unlucky? Or am I able to re-load my world and get those last 2 for it to count? Not gonna lie, this is a bit ridiculous.

Yes, just restart the session and try those places again.