I don’t want to include spoilers for this quest. After you defeat a certain someone and have to return to Markos when he is up top underneath the statue it is no longer possible to teleport or walk beside him. The terrain doesn’t register as a tile you can move to (no blue squares when using the teleport feature or unable to free walk in either). This means you can’t actually wave at him to turn in the quests. There are several other players currently stuck because of this as well.
He has the icon so I don’t think he’s bugged or anything. You just can’t reach him.
A few players have managed to actually walk (within their room) to get to him, but my play area isn’t big enough to do that so myself and a few other players are still locked out of doing quests at the moment.