ESP8266 Thing Dev Board Problem waking up from deep sleep after 30 minutes

Hello,
I have programmed ESP8266 thing dev in following way:

  1. Take the temperature, humidity reading using DHT22 sensor, store the reading in RTC memory and go to deep sleep for 30 minutes.
  2. Wake up from deep sleep after 30 minutes and again take the reading, store the reading in RTC memory and go back to deep sleep.
    3)Repeat this process for a total of three readings.
    4)Once we have three readings, post the data to ThingSpeak Channel.
    5)Repeat the entire process.

The above process work fines for the first cycle but after first cycle esp8266 doesnot wake up at all because I don't get any reading on ThingSpeak Channel. However, if I reprogram my board with a deep sleep timing of 15 minutes or less. It works fine.

I am totally confused what is the issue. Can anyone please point me to the right direction. Thank You!!