The default timeout value for the Load Balancer (60 seconds) is too small (as configured in IIS).
Change the timeout values for the IIS to the default value (20 minutes), if possible.
The interval for the Job Calls is configured in Jobservice.cfg (the job service configuration) and the default value is 90 seconds. Timeout values shouldn't be less then this default value.
Change the timeout value for the Load Balancer to at least 90 seconds.