“NoPhear” already wrote: “No ath displayed, but progress still increases”, so he has no issue with assigning the Tracker. This is a known problem with Tracker UI for Join In Progress Players that is like this for many months. See for example this thread (or you can find many more about this):
It was supposedly to be fixed in update v33.10, but it was only improved a little bit = Tracker UI is still not reliable and some players in some maps will not see any Tracker UI on the HUD when they join a session in progress no matter what (while their tracking functionality will normally work for them in the background - they will not see info about their progress on the HUD which is really very bad for User Experience if you are using them for something like Challenges or Quests so you really need to have them visible).