Almost the same problem for me. I started making a quest, set the alias for an NPC and had made him the quest target. Target marker won't appear in game. I have tried to change the location of the reference of this NPC, but it won't solve the problem. Very confusing is that I have a quest already made where the marker on the NPC is no problem. Don't understand what I changed this time to make this problem appear. Thanks for all help that will come eventually along.