UMMAU42 is an unknown user in the hypergrid. Nevertheless the user exists and teleports. Here comes the dialogue, March 9, 2017. Hypergrid Safari.

Thirza Ember: Mostly, we were growling over the ongoing UMMAU issue – that’s when the name of an avatar doesn’t appear above their head, and the tag reads UMMAU42. This has to do with the fact that when your avatar arrives in a region, your viewer and the region begin communicating. The region tells your Viewer about all the people, objects, textures, scripts etc that the region contains. At the same time, the region is asking for information – not only the appearance of your avie, but also the contents of your inventory – the stuff in your suitcase, and (mostly because OSGrid doesn’t use the My Suitcase Folder strategy) the Region also tries to read everything in all your other inventory Folders – it can’t, but it makes multiple attempts before giving up.
Now, that’s a lot of back-and-forth communication for the server to handle, even if it’s just one avie entering a region. Imagine the amount of data exchange that happens when 20+ people teleport in from all over the hyperverse. Even more stress on the server if someone has an attachment that has some funkiness about it, like they didn’t put it in their My Suitcase, or it’s flawed mesh.
Eventually, when the flood subsides, names will show up. Sometimes, you can force names if you Friend or check the Profile of the person who appears as unknown, but… this is why devs smile at you when you complain about UMMAU.
Kiely Kjeller: what does the ummau stand for anyway? probably something like UFO, hehe
Sunbeam.Magic: it might mean You Might Miss Avatar Unavailable ???

And the 42? Must have been generated by42!