Yup, pretty much what EndBringer said. If an emperor abdicates without losing all their keeps, they become a 'Ghost Emp' and that faction cannot claim emp until they lose all their emp keeps.

A while ago I wrote a simple script that would tell you which faction had ghost emp. I think it should still work, so if you copy-paste this into your ingame chat then it should tell you who has ghost emp. (only works on PC/Mac)

/script local alliance,_,name = GetCampaignAbdicationStatus(GetCurrentCampaignId()); local alli = zo_strformat(SI_ALLIANCE_NAME, GetAllianceName(alliance)); if alliance == 0 then d("There is no Ghost Emp") else d(name.." of the ".. alli.. " is the Ghost Emp") end