.net - WCF service doesn't send response, but doesn't error either -

i'm running strange behavior wcf wshttp service finishes processing data (i know because log message right before return list of people) client doesn't receive response , sits there "hung". increased timeout 2 hours , though service finishes retrieving data after 20 minutes, client hang 2 hours before reaching timeout limit , receiving timeout exception. guessed, returning lot of data service (about 50 thousand complex objects). have [datacontract] attribute on want serialized.

troubleshooting i've done:

1. in our test environment service seems work everytime , returns after 20 minutes.

2. our production servers randomly run above issue. returns after 20 minutes, client receives timeout error hour , 40 minutes after service finished.

3. i enabled wcf tracing , last thing traces close clientbase statement. last thing before returning method (except log statement right after that).

4. i set config settings max values handle large dataset being returned.

is server/network issue? other steps can take track problem down?

the service hosted in iis7 windows server 2008 r2. using .net framework 4.5.2.

it looks load balancer issue. had increase response timeout (and maybe response size) on load balancer. not sure these settings on lb because our network admin made change.