Strange 502 Bad Gateway error

Hi guys. I'm very sad because since OC 10 mi installation is a bit "crazy". Well going straight to the point. After days in restoring my small server from scratch i had all up and running. Linux,NGINX,MySQL,PHP, WordPress, and latest 10.0.3 OwnCloud. Ok my latest support request was workaraunded the end CloudFlare has issues with all the environment. Well i'm pragmatic my site is personal and safe enough so i got over this problem. What's new? Till yesterday all was working i mean the web interface, login, files, sync and all. This morning i found the OC sync client "gray" so what happen? Well i tried to open the web interface and the i received the 502 Bad Gateway error. Obviously you think about a nginx failure, a server failure you imagine a lot ....but doing a fast test nginx was running, wordpress as well, mysql , myphpadmin all except OC. I ask to myself "how come"? OC itself is a web app as well as wp. So how come all was running except OC? I mean i didn't touched nothing in those days neither system upgrade yesterday was all ok today only OC down. I'm not a GURU in Linux but i would like to understand. As long as i know "The 502 Bad Gateway error is often a network error between servers on the internet, meaning the problem wouldn't be with your computer or internet connection." That means that it should impact all the web services running on it. So this is the mistery : how come from a day to another without touching nothing "only" OC reported that error? Well ok a simple restart of the server solved all i mean now also OC works again with any issues or error...How all this can happen? Why? I'm just curious.

Maybe the following page helps you to understand the situation: