Occasional 504 error, most definitely no issues at our end

Nobody else has responded, so I’ll give it a try.

Are you getting the pretty Cloudflare error screen? The Support docs say it’s getting the 504 from your server, but you say there are no error messages. I know you said you have two domains configured the same way and one is ok.

Could there be a firewall that’s triggering and blocking access?

Is this on the busier of the two domains?