Problem with application load balance that I cannot solve

We have an application load balancer with one instance but scales to 8. My problem is this. I have three mobile applications that log into the instances with POST and json and one of the applications can no longer log in. It logs into the test server that is not on the load balancer, but on the production server, it gives 502 bad gateway sporadically at first but now all the time. The server is not returning bad data because it works sometimes, it seems to be a problem with the load balancer not forwarding requests to the appropriate url. Can somebody give me a clue where to start dissecting this. I have looked at the code, I have looked at the application, and I have looked at the server, and the problem seems to lay with the load balancer just not cooperating for no reason given. Like I said, the other two applications work fine and they all share similar code. I just. found out about it from apple about the problem with the login and this 502 bad gateway error will not go away. Any help with 502 gateway errors would be appreciated. I have increased the timeout on the server, I have tried rebuild the load balancer which worked yesterday for about four hours then quit. I am at just a loss. Thanks in advance.