[Multisite] Complicated Redirect Loop

I am getting a complicated redirect loop on the mentioned site. I cannot log in to the admin side as well. I've tried a couple things including:

1. Resetting the .htaccess file to default.
2. Emptying the .htaccess file.
3. Disabling all themes, plugins, and mu-plugins (renaming respective folders inside wp-content).
4. Making sure wp-config.php is okay.
5. Checked site URLs in the database.

The mapped domains for subsites are still loading fine though.

Please advice.