Well, I just got the 504 error message again.
This is now beyond ridiculous.
I cannot believe that both capnel and WHM backups cause a dedicated server to lock up and refuse to respond every time it does a backup. If that was the case, millions of websites would be down.
This same server used to work just fine using HostGators own WHM automated backup to a 2nd disk, and also using siteautobackup.com
I suspect it's only since the server was switched over to 64bit and all the performance tweeks have been made that the problem has arisen. I could be wrong, but it most certainly used to work just fine with no reports of 504 gateway errors.