I played against three players whose named showed up as "Player###", i.e. "Player272", in the score board and over their heads. Checking their steam profile revealed that their real nicknames all started with the unicode character U+1F5A4U+FE0F (can't paste the actual character because it breaks the forum).
I played several matches against them and the bug occured in all of them. The numbers in their names changed from match to match though.