[Elemental earth]/exact returns nothing, but elemental earth without exact returns it. I imagine there are other items like this but haven't come across any yet.

I wonder if it has something to do with the item id?

all elemental x, essence of x doesnt work

same thing with stonescale oil/eel

I had the same issue and fixed it by running

/aux clear item cache

Weird is that I fixed it yesterday and today I had to run the command again because the bug accured again.

yea, it helps

I can't reproduce it. Could be because some item data change with the expansion and yes /aux clear item cache will help for that. @Deamp if you quit the game without a regular logout (or having done /run ReloadUI() before) then you lose all changes in the addon savedvariables (this is behavior of the wow client which addons cannot influence), probably that's why you had to do it again.