I'll repost what I posted earlier since some missed it, but this is what the guy is saying:
1st chest - Ascendant materials one that you can't miss.
2nd chest - Spirit Bloom chest in Templar room after you kill him (although some say they've gotten ascendant mats from it as well).
3rd chest (potentially new chest) - Along the path from the Spirit Bloom chest room that leads to Gorgon cave. This chest apparently has ascendant materials/legendaries/exotics.
4th chest - First Gorgon cave chest that has ascendant materials/legendaries/exotics.
5th chest - Second Gorgon cave chest that only has ascendant materials.
Apparently other people in that reddit thread said they found the room this guy's talking about, but the chest wasn't there for them. I'm thinking that either A) this dude is lying or B) this chest is on a timer before it despawns or it can spawn in multiple places.