Recently I started to experience this redirecting issue. Not sure what caused it and I'm guessing either the wordpress update or from the theme update. I am using Flatter as child theme and Clipper as parent. Only the Clipper theme was updated to latest 2.0.6 version.
The redirecting issue I am experiencing is right after logging into wpadmin. After I input my wpadmin login credentials and click log in, it redirects to this url: https://XXXXX.com/wp-admin/admin.php...&firstrun%20=1
. Instead of going to the wpadmin page. Any idea how to fix this?