Playing on Mortal Empires as Clan Skryre and have confederated clan pestilence (lord Skrolk) before he hit level 6. When I get lord skrolk to level 6 the quest for the Libas Bubonicas is not added to the quest chain, nor is the item automatically added to available inventory / equiped on him.
I have looked into the quest details and I believe it requires you to build a pox cauldron building and use a rite of pestilence, both of these actions are available as clan Skryre.
I have reloaded a save multiple times in the hopes that it would eventually trigger the quest but it has not triggered any of the times.
I have already found this issue reported when playing as clan Eshin, but didn't see any posts about Clan Skryre.