Hi @aaron25,
As you noted from the error page, a 521 usually indicates a problem with the origin server, rather than with Cloudflare. A 521 error happens when Cloudflare is unable to make a TCP connection to your origin server.
This Community Tip has most of the common causes. As you are seeing this error intermittently and from specific locations only, my best guess would be that your server/host is doing some rate-limiting/blocking of some of Cloudflare’s IP ranges. You should make sure that Cloudflare’s IPs are allowed through any protection you have on your server to avoid this.