This article applies to you only if you are using Cloudflare.
Issue: when trying to access the admin area (example.com/wp-admin/ or example.com/wp-login.php) of your WordPress site you are getting the message:
This page isn’t working
example.com redirected you too many times.
Try clearing your cookies.
Notice that the main address example.com is working correctly.
Fix: the issue is caused by your Cloudflare settings. Steps to fix:
1. Log into your Cloudflare account
2. Navigate to the SSL/TLS section
3. Here, enable the Full option (Encrypts end-to-end, using a self signed certificate on the server)
4. Wait a few seconds and access the admin area again. Everything should be ok now.