We are having an interesting issue with an API integration into our TFS 2013.3 system.
We have an internal custom web service that calls into the TFS API. When running the custom service under an AD account created specifically for this purpose (uses pass through auth when talking to the TFS API using DefaultNetworkCredentials in the code) all calls take their time to execute + 30 seconds. When I switched the app pool account for the service to use my own personal AD account that 30 second delay disappears. Inside TFS the accounts have almost identical privileges and assignments and the calls with the delay still succeed with no obvious event log entries pointing to any issues. The only obvious difference is that my account is a local admin on the server while the intended service account is not.
Currently this issue is blocking us from performing out production TFS installation and this is for a national bank so getting our account security correct and clean is highly critical.