On my MoPremix character Haävi-Barthilas I have unlocked the final Infinite Power achievement (4200 threads) however my achievement progress still has Infinite Power VIII (500 threads) as not completed.
This is impacting any alts I create as they are not correctly having their cloak baseline improved through these achievements as I can only assume 400 threads is the last one taking effect. (XP gain is only 16%)
I’m having a similar issue, except I just hit Infinite Power VIII and am not showing completion for Infinite Power V
Same exact issue here. I have completed the Infinite Power XII (12) achievement (the final one), but VIII (8) is still showing incomplete.
Very similar issue here… oddly, it’s Infinite Power IX that’s not triggering for me.
Character in question is Raadiran on US-Thrall
My wife’s character (Ishaena on US-Thrall) is also having the same problem with Infinite Power IX not triggering, and she’s got XII done.
Same issue here on Exodar - Main TR character has Infinite Power XI completed (and in said achievement, it shows VIII being completed), however in the achievement list I can see VIII as incomplete.
Same issue with alt, I created one and it feels like the cloak is lacking stats vs. what it should be at.
Same issue here on my Shaman on Area 52. I’ve gotten to XI so far and VIII hasn’t completed.
Same issue here too
Same issue, didn’t get VII even though the rest after are completed so now my alt didn’t get the right cloak values 
Same issue. I opened a ticket and all they did is send some nonsense response about loot recovery.
Same here. 2500 threads and IX (600) + up are not activated.
Same issue as title states. No matter how many threads I collect it never completes.
To update the status, my ticket has now been forcefully resolved and I still don’t have the achievement.
Currently levelling an alt and seeing if I can trigger it’s completion on that character or if it’s just screwed.
Haven’t had any other earlier achievement for threads trigger yet, so I’m not hopeful.