KONG community edition (2.0.0) docker image - lot of 504 Error

We are getting randomly lots of 504 Error but could not find the reason for this error., As we do not see any 504 error or taking long time in upstream service. We suspect the request is not even send to upstream but it return back to consumer 504 by KONG.
Really KONG logs are not helping. Any suggestion to enable more log. we enabled debug level also.
we set higher upstream read write connection out. (120000)
All 504 connection time ( upstream_response_time is around ~10.000) out is
“upstream_response_time”: “10.003”,
“request_time”: 10.002,
“bytes_sent”: 381,
“body_bytes_sent”: 132,
“status”: 504,

What could be the cause ?
nginx_http_upstream_keepalive_requests , nginx_upstream_keepalive ? anything needs to be tuned .

No one reading or responding ?

@ramyogi could you solve the problem? something similar happens to me …

So far could not find any resolution for this and no one helping for community edition so unfortunately have to decide to go for enterprise edition atleast to get support.