Cant reach my test page

Since today I have an issue when loading my test page - after entering the login credentials to enter my site,

saying; 

upstream connect error or disconnect/reset before headers. reset reason: overflow

After reloading a couple of times, it works again. 

Anybody any idea what might cause this?

Hi Rudolfo, Did you happen to work out how to resolve the issue? I'm getting the same message when I try to look at the contact section.