Since a recent update (not necessarily the last), I have been unable to log into the /wp-admin section of any of my sites that use Defender.
I do not have WP-login lockout enabled. I tried whitelisting my IP and also the localhost without avail. I also tried activating login-lockout. There are no errors produced in the Apache/PHP log: it appears to be a hanging function.
This is likely due to my server configuration. I use HAProxy to terminate SSL, then it consults Varnish cache, which then asks Apache for PHP computation. This means that many transactions take place on localhost and IP tracking terminates with HAProxy.
I have had to disable Defender on all of my sites. I will not be troubleshooting this issue as it would cost me too much money. I am writing this to inform you. If you check the diffs, surely you can find a function that'd hang without a client IP or what not. The issue occurs reliably with login, but it also sometimes hangs with updates and other pages.