Invalid player nicknames are now set a bit differently. The purpose of this update is to add more consistent nicknames.
Instead of adding a '_P#' suffix, illegal characters are now replaced with a question mark character.
Nicknames that are too long will be trimmed and an ellipsis suffix will be added.
The way guest IDs are assigned was also changed.

Because of these changes, we recommend your username not to contain any question mark characters, however it is not prohibited.