After buying a Conq PvP neck (Crimson Glad Necklace - The haste one) I was unable to use the Tiered medallion settings on the piece saying it is ineligible. Strangely this works on my mastery version of the neck.
Update: Tested with other pvp necks from conq vendor. Unable to apply. Tested with honor versions, able to apply.
You can’t apply them to the new neck from the elemental invasions either.
This is also happening to me, I bought the haste/vers conquest pvp neck and cannot apply any of the R1/R2/R3 tier medallion setting to it.
Same problem I bought a conquest mastery necklace and I can’t put settings on it at all. All it says is cannot modify.
This also has happened to my Mage. Got Glad neck from vault and bought tiered settings only for the neck to say it’s an invalid piece.
Same.
Just adding that doing arena and getting wins over 1000 and even upgrading the item with honor won’t allow you to add a tiered setting.
Same thing happened to me today
Same thing here, i deleted it and restored it and it still doesn’t work
Same issue here, did you guys upgrade your trinket with honor as well?
I also suffer from this malady
Same. Can’t add sockets to crimson glad neck
Tried putting the Storm-Charged Manipulator from vault onto a conq belt I just bought today and it doesn’t work. It works on any other belts I’ve acquired before this week’s reset though
Same issue as all of the above - brought a new pvp neckless, couldn’t put any tier settings in.
Bought a new ring on another character & couldn’t apply storm-charge manipulator to that either.
Created a ticket to blizz, who kindly closed the ticket as completed & sent me a ‘friendly link to support pages’ and bumped my ticket to the back of the queue for the trouble…top notch customer service from a multi-billion dollar organisation 
Tried this too - didn’t work, tried selling back to vendor & buyback, also didn’t work.
Same rip, shouldve got a cloak instead
Me too m’lady tips fedora
The same has happened to me.
Same thing happened to me with a Crimson Gladiator’s Necklace 402 (7/9)
same, hope for a hotfix not 2 months long wait ;d
Well add my name to the list…I’m a casual so 3 gems and 3 medallions for the sockets is pricey to me…and I can’t even use them atm cause of this bug. Hopefully it’s a quick fix.