Infura behind a NGINX randomly fails with 403, 404 or 504

[bb4L]

Since yesterday evening (CEST)

We experience infura not always responding from behind our NGINX proxy, when it fails we get either a 404 or a 504 without any further information

or a 403 with

{
	"Message": "User: anonymous is not authorized to perform: es:ESHttpPost because no resource-based policy allows the es:ESHttpPost action"
}

the nginx server conf is similar to the following:

server {
        server_name SERVERNAME;
        listen 80;

        location / {
            proxy_ignore_headers "Set-Cookie";
            proxy_hide_header "Set-Cookie";
            proxy_hide_header "Access-Control-Allow-Origin";
            proxy_set_header "Content-Type" "application/json";
            add_header Access-Control-Allow-Origin *;
            proxy_pass https://mainnet.infura.io/v3/APIKEY;
        }
    }

any ideas why this started to happen or how we can fix it?