I just encountered a bug that has reset my Forgotten Knights progress to rank 0, but I am still on the quest step to defeat Aberroth. In the screenshot below you can see that I am simultaneously rank 0 while also having the defeat Aberroth step on the screen.
I’ve logged out of this character, logged out of the game completely, verified file integrity on Steam, and changed zones. Nothing has brought my rank back.
Update: I attempted going through an emp mono and summoning Abom to see if that would affect my rank. The game didn’t summon a harbinger and I’m still stuck at rank 0.
Update 2: I also tried going back to a regular monolith and was still unable to summon a harbinger. I’m out of ideas to try and my character is unable to progress in Forgotten Knights, cannot summon harbingers and therefore cannot progress to Aberroth.
Update 3: I switched to another character and was able to summon a harbinger. It only increased me to rank 1 and the game believes that my highest corruption kill was only corruption 0. https://imgur.com/a/5AsLWpP