I'd suggest to control the cache:

With nginx errors --> On Internet I've found these possibilities among the others:

Nginx running as proxy for Apache web server.
Nginx running with PHP-FPM daemon.
Nginx running with other services as gateway.
Bad buffering/timeout configuration.

Last months I received the same message more and more. In the last two weeks this error desappeared, but eventually returned in the last four days.

The complete error desciption is
502 Bad Gateway nginx

Is there a problem on the gateway?
In my case the other sites are working good without any message. I tried also to clear the cache in the browser but the problem sometimes will eventually return.

Is it a configurations issue?

Mi congratulo con te!

Ok, I just got back from the battle and, yes, I agree with Guybrush88. OK, sorry, I have to go back to the battlefield

Thank you.

Con l'aiuto di tutti cercherò di essere d'aiuto anch'io.

Thank you very much. With your help I'll try to do my best.

Grazie infinite, con il tuo aiuto cercherò di fare del mio meglio per dare una mano a mantenere questo importante progetto.