Adding my bit to this. Unlocked Rank 5 of Korthia gear on a toon, can’t upgrade a piece to Rank 5 on that same toon (even though I upgraded other pieces to Rank 5). Also can’t upgrade a dungeon ring to Rank 10 (everything else I could upgrade to rank 10.)
Also a friend of mine with 1600+ rating can’t upgrade a new piece of Unchained Gladiator gear she just bought.
Granted it’s from BFA, I cannot upgrade any Benthic gear in Nazjatar since the new Gear Upgrade UI was released.
I found a solution to my issue, I unequipped the new item which allowed me to upgrade something else, then I re-equipped it and everything is behaving normally again.
I am also having this problem. I tried taking off my equipment and putting it back on. I have gone to other upgrade stations and still I have a problem. It has been 2 days now. It is a little frustrating. This is not PVP gear.