A few things:
This page does say the username is case sensitive. Is it really? https://www.mediawiki.org/wiki/Help:Logging_in
I do not see a reset password or request for temporary password on the login screen as it described on that help page:
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What if I forget the password or username?
Your username is case sensitive. If you enter an email address when signing up for the account, or in your Preferences, you can make a request on the login screen for a temporary password to be sent to that address, which will allow you to retrieve your account. If you did not enter an email address, or the address was out of date, you will have to create a new account under a different username.
----Instead I only see this when typing in my email address in the username box and leaving password box empty: