So, In tracking down the problem with the Stardust Spire sub-achievement, I ran into a broken questline. I thought all I had to do was finish "Check in on the Edunes" because that was a precursor listed for "Three Friends of the Forest", but running the questline stated to get that quest did not open it for me. On that note, it did lead me to a quest that put me at the location of the same name as the sub-achievement, so here is the questline that I believe is at least a part of the requirements for Stardust Spire:
- Bathran's Hair
- Delivery for Orendil
- Bathed In Light
- Orendil's Cure
- Elune's Tear
Followed by:
- Dryad Delivery
- Search the Bole
- Playing Possum
That unlocks:
The only quest at Stardust Spire that I didn't attribute to another previously known questline was "Retaking Mystral Lake" which upon completion still didn't give me the sub-achievement. Finally, after completing "The Goblin Braintrust" it dinged the sub-achievement.
At this point, I have no idea whether the following quests are a part of this line or not, even though they seem to be currently linked to this sub-achievement, and I have completed them, I don't think they are:
- Three Friends of the Forest
- In a Bind
- Clear the Shrine
- The Last Stand