[Baertram]

Event_zone_changed does not fire for all changed zones afaik, only if you are e.g. inside a city and step out to the worldmap again etc.

Try EVENT_PLAYER_ACTIVATED instead (fires after login, loading screens where you changed a zone etc.). You can do the zone check there, by using
API functions like

local zoneIndex = GetCurrentMapZoneIndex()
--Either:
local zoneName = zo_strformat(SI_UNIT_NAME, GetZoneNameByIndex(zoneIndex))
--or if you also need the zoneId:
local zoneId = GetZoneId(zoneIndex)
local zoneName = zo_strformat(SI_UNIT_NAME, GetZoneNameById(zoneId))
 
--Parent zoneId is the id of the parent's zone, e.g. if you are inside a delve in Alik'r Desert the zoneId is the one of the delve and the parentZoneId is the one of the zone (e.g. Alik'r)
loca parentZoneId = GetarentZoneId(zoneId)

etc.