Yes, they display no image on the activity tab, and when you click them it is given as an "unknown observation" with no details. This is obviously due to how the site "downloads" this data. Recent observations load very quickly, while those from a year or earlier may take up to half an hour (!) to load.
I also note that even if they are "loaded", they will not show unless you go to your sightings, and then switch back to the activity tab (at this point any notification that has fully loaded will then refresh and show the details).
But yes my issue is that if I view an observation (through the notification link), it will clear that notification even if I can't see it...an for older ones, I don't have the patience to wait 5 minutes or more for it to load, so it becomes lost in effect.