Requiring entropy in the username? What? I can understand the password, but what site requires you to put a symbol in your username?
> lowercase or capital letter, a number, or one of these symbols _.@/-."
says "or" and not "and", so it doesn't actually seem like there's any issue so long as you include a letter. Then the only real restriction is the minimum of six characters.
In other words, the sign up page text, the sign up page JS validation, the back end database, and the trouble logging in page ALL have different requirements just for the username.