i could send my esp to deepsleep successfully for 30 minutes in each iteration,
i.e: ESP.deepSleep(1800000000, WAKE_RFCAL);
i am sure that it is in deepsleep for 30 minutes. after each wakeup it is processing some data and sending to server. i can see the information in database for every 30 seconds interval. may be ur esp sdk version is not the latest.
Thanks.