Often, when logging in to agent domain, my Agent name is missing over my avatar. This can happen on login and also on TP. I have attached a picture from today on login, and an older viewer log file when I added some debug prints when I first noticed it.
The viewer will get two objectupdates from the region that contain the FirstName LastName. The first time the names are correct, then the second time the names will be blank. Depending on caching in the viewer, you may or may not immediately see the change in your viewer window. On Windoze, Alt-Tab between some different apps that overlay the SL viewer window can usually flush it out to be visible.
The viewer shouldn't be getting objectupdates that contain blank FirstName LastName