For the quests: "Meet with Istiana" and "Meet with Arzagos", neither of these NPCs are present in their respective cities (Epicrotea and Marunath). The quest worked fine in my previous save, which was on 1.5.7 beta. The problem has only appeared in a new campaign started on 1.5.8 beta.
I will upload the save file at upload.taleworlds.com
I will upload the save file at upload.taleworlds.com