In my current game I lost standing with a vassel for not attacking "Chu". He was at war with Shu and I immediately attacked mistaking the spelling, On the net turn I still had a reminder to attach "Chu" so I did a thorough search and there was no such faction.

Does anyone know anything about this? Perhaps a pending fix?

There's a faction named the Chu and another faction named Shu,

Most likly your vassal had allready contact with them but you not, the Chu are vassals of the Shu or they allready made peace meanwhile.
Everything aside from Citybuilding&research isn't very polished, esp. dimplomacy&warfare...expect more like this.