admin creates new users - issue with username

Hello,

I created new users at www.mysite.com/admin/user/user/create

Half the time the username was created as the text before the @ in the email, so the link of the username shown when hovering over the username at www.mysite.com/admin/user/user was correct as per my pathauto url to each user page => www.mysite.com/user/bond007 => where bond007 is the username from bond007@xyz.com

But the other half of the time the username looked something like mkdielgh, and the usernames when hovering over a username at www.mysite.com/admin/user/user shows the link as www.mysite.com/user/mkdielgh => I don't know where this random string of letters is coming from.

Of the 10 new users I created - half was ok and half was not.

Can anyone please assist?