The Cloudflare redirect loop error is something we see at least once every day in support. Fortunately, it is easy to fix and prevent once you know the cause.
This is a Cloudflare specific issue. They state:
The FlexibleSSL encryption mode in the Cloudflare SSL/TLS app Overview tab encrypts traffic between the browser and the Cloudflare network over HTTPS. However, when the FlexibleSSL option is enabled, Cloudflare sends requests to your origin web server unencrypted over HTTP. Redirect loops occur if your origin web server is configured to redirect all HTTP requests to HTTPS when using the FlexibleSSL option.
How to Fix and Prevent Redirect Loops
First, enable an SSL for your website inside of your GridPane account. Only enable this option after an SSL has been fully provisioned for your website on your server.
Please use the Full (Strict) option. This ensures a secure connection between both the visitor and your Cloudflare managed domain, and also between Cloudflare and your server.