If application developers are complaining that east-west server traffic is not being load balanced, there could be several reasons for this behavior. BGP multipath is crucial for allowing multiple equal-cost paths to be used for load balancing, so if it is not configured, load balancing would not occur effectively. Policies for load balancing need to be configured to ensure that the traffic is distributed across multiple paths. Lastly, configuring ESI active/active is necessary for ensuring that multiple links are active and can be utilized for traffic, which aids in load balancing of east-west traffic in a data center. Insufficient spine to leaf bandwidth (option D) would affect the overall performance but is not directly related to the load balancing mechanism itself, and MP-BGP exporting the correct prefix type (option E) is more about ensuring proper route propagation rather than load balancing specific traffic flows.