504 gateway Timeout issue

Greetings!

May I ask is this website behavior still happening or has been resolved in the meantime?

I am sorry to hear that you are experiencing issues/errors with your Website while using Cloudflare service.

It could be that your origin host / server obviously cannot handle all the requests made to it (be it for example PHP, etc.).

Have you tried contacting your web hosting provider so far?

In terms of the stated error you are experiencing, may I suggest looking into below articles:

UPDATE:
Seems you are using Laravel app (uses and requires PHP at the backend to handle all the requests)