That screen would indicate there is an issue with your server somewhere. You would need to check your server error logs on that. I cannot tell you more than that from that screen, as cloudflare provides a catch all error of 520.
With regards IP address, we can only show what your server shows. Its very likely cloudflare is masking the IPs by proxying them. You can bypass this by switching on this setting - "Trust IP addresses provided by proxies?" , which can be found here
System>Settings>Advanced Configuration