502 Error after update

Hi there,

I have troubles with sending forms on one of my pages. I have done all the latests updates and for me all works well, but for some reason I get Bad Gateway 502 Error from various people who tried to send the form.

Where could be the issue? I already contacted the server provider and they said there must be something wrong with the scripts … Server runs on PHP 5.6.

Thanks for your help.