I submitted an email on the modX site about this issue, as well. I have gotten a 502 bad gateway error intermittently for the past 3-4 days while trying to access Revolution documentation online at
rtfm.modx.com. I can now not access the site at all. I've cleared my browser cache and tried multiple browsers. This is a problem with the modX server(s).
Is the documentation for Revolution and its main add-ons available via other means?
It is working for me, anyway you may try with google cache until they fix it.
