Well, after copying the 'name' from the browser debugger (tried both Firefox and Chrome, latest non-developer releases), my text editors say it's a set of 4 and 5 0x1A characters (26 decimal, ASCII symbol 'Substitute', or ^Z/Ctrl-Z) separated by a space, quite unlikely that's a real name, whatever encoding or character set it might be, must have a deeper meaning, as ^Z used to be EOF (End Of File) for text files, way back when...
The only rendering engine that is actually showing something (and installed on my laptop) is Chromium (Chrome/Vivaldi), neither Firefox, Edge or IE show anything, so that might make Chrome-based browsers a tad more informative.
I would have expected SMF to filter out/reject any non-rendering characters from usernames, but obviously that's not a test-case for them.