This issue started happening after we update the latest 1.11.3 version recently on ubuntu16.04 server. We didn't touch any of the nginx default configurations during this update.
Attaching the configuration for

Error
2016/09/10 05:28:04 [warn] 5214#5214: *107595 upstream server temporarily disabled while connecting to upstream, client: 192.150.10.205, server: _, request: "GET /resource/js/backbone_overrides.js HTTP/1.1", upstream: "https://x.x.x.x:443/resource/js/backbone_overrides.
This error is coming when the nginx is trying to fetch some resource from a backned server over https .

Thanks
Tarun