Does the root domain point to the same location as the www? Right now Cloudflare is reporting a 521 error for the root which seems to indicate the origin isn’t responding. Couple of suggestions below:
A 521 error happens when Cloudflare is unable to make a TCP connection to your origin server. Review the suggestions in this Community Tip for Quick Fix Ideas.
If your domain works when you visit www.example.com, but not when you just visit example.com, you may want to redirect your root domain to www using a page rule. You can follow this community tutorial on how to do this.