I use Australia Post MyPost Business for sending items.  A long-running problem in this system may be related to what is being described here.

Inside the MyPost website if you click on a parcel in the Tracking tab it almost always says they are experiencing technical problems and there is no tracking history available at the moment.  Those that do work have no tracking history beyond "Initiated" and I have to go to the public website to look up tracking to get any useful info.

So I'd say that eBay cannot get info for some tracking numbers, resulting in this behaviour at eBay.