Map Completion Not Granting Chests
Did you already get the map completion chest for that map? they constantly add pois and waypoints and hearts to old maps. it will lower your percentage down past 100%
What Therodin said. You can only get completion rewards once. If you go back and get newer POIs and whatnot after completing the zone (or after finishing the entire world completion), you won’t get the reward a second time.