It seems the seasonal quest line has a problem at its end. If you complete it on a World Tier higher than 2, you won’t get the base Invoker of Varshan recipe. This will then prevent you from crafting higher level ones.
Many players have been reporting this issue for the past few days on the official forums. They completed the seasonal quest at World Tier 3 or 4 and received a higher level Invoker of Varshan (Foul or Tormented). However, they did not get the base Invoker of Varshan. That recipe is required as you need that crafted item to created the higher tier ones, which basically means you can’t progress that part of the season journey and fight Varshan at all.
Players are reporting that there is a solution, however, but it’s a little problematic. You can re-roll a new seasonal character and get the questline done in World Tier 1. This isn’t actually going to take a long time either, as you can be done in around an hour and a half – but you’ll need a higher level player’s help as part of the quest involved a fixed level 35 Stronghold area (which includes a level 40 elite). Once you learn the base Invoker of Varshan recipe on your second character it will be unlocked on all characters. You can then progress normally with your mains. We’ve also seen one report of a player not getting this method to work, but the vast majority are reporting it fixing the problem. So take that into account.
Hopefully Blizzard will fix this issue soon as well and remove the extra steps necessary.
You can also check out our full Invoker guide here, which covers all the steps involved from above.