Cowboy drop some packets on port 80 - http

Question

i am running application in elixir plug and when i run this api app on port 80, it drops some packets and respond 400 bad request directly from cowboy, it is not even logging or anything else. when we debug it , we found that, some of the header values being dropped when getting cowboy request handler.
we are running under AWS load-balancer, when we run both on 8080, every thing is perfect but when we put on 80 packet starts dropping, can any one know workaround this ?
We made a first request:
"POST /ver2/user/update_token HTTP/1.1\r\nhost: int.oktalk.com\r\nAccept: /\r\nAccept-Encoding: gzip, deflate\r\nAccept-Language: en-GB,en;q=0.8,en-US;q=0.6,it;q=0.4\r\nCache-Control: no-cache\r\nContent-Type: application/json\r\nOrigin: chrome-extension://fhbjgbiflinjbdggehcddcbncdddomop\r\nPostman-Token: 05f463a4-db55-6025-5cc1-f62b83db7c93\r\ntoken: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoxNH0.Ind--phmd5saXMjBVjgRKNcCEL60qZoCbHggu-iAqY8\r\nUser-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.71 Safari/537.36\r\nX-Forwarded-For: 27.34.245.42\r\nX-Forwarded-Port: 80\r\nX-Forwarded-Proto: http\r\nContent-Length: 103\r\nConnection: keep-alive\r\n\r\n"
Response for the first request: 200 OK
We made the same API call again as a second request. What we saw is the the content-length of the previous packet is 103 and the first 103 bytes is not seen in the next packet. I guess the system thinks the first 103 byte belongs to the previous packet itself.
"e\r\nAccept-Language: en-GB,en;q=0.8,en-US;q=0.6,it;q=0.4\r\nCache-Control: no-cache\r\nContent-Type: application/json\r\nOrigin: chrome-extension://fhbjgbiflinjbdggehcddcbncdddomop\r\nPostman-Token: 0e52f1b6-120a-c321-2ba4-d6d20d5eb479\r\ntoken: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoxNH0.Ind--phmd5saXMjBVjgRKNcCEL60qZoCbHggu-iAqY8\r\nUser-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.71 Safari/537.36\r\nX-Forwarded-For: 27.34.245.42\r\nX-Forwarded-Port: 80\r\nX-Forwarded-Proto: http\r\nContent-Length: 103\r\nConnection: keep-alive\r\n\r\n"
Response of this : 400 bad Request which i see because the first dew bytes are missing.
We are using Elixir.Plug and cowboy

Answer 1

For others that find this question (like me) make sure you're not ignoring any returned conn structs from the Plug.Conn functions.
This snag is outlined fully in this issue, along with a gif illustrating how this goes wrong.