Trouble Logging In and Out of wp-admin on Long Established Site

Yesterday my client advised that she was having trouble accessing wp-admin on the site at I have been playing with it for about 12 hours and can't figure out what the problem is. I have rename wp-login.php set up via All In One Security, and I have also added the rename wp-login.php separate plugin.

I have done a complete plugin conflict test and have changed themes. The issue is intermittent. Sometimes I can login at wp-login.php. Sometimes I can long directly at wp-admin.

What happens is that when I put in username and password, when it loads, they just disappear.

I have tried removing .htaccess. I have verified that all is good in wp-config.php. My users still have admin roles. I have not added any new plugins (with the exception of Rename wp-login.php after the fact).

The same thing is happening with and
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