Hi, I can tell you why.
First word, I guess your app seems not update for year. From Aug 1st, 2014, Google update its policy to not allow Ads network (such as RevMob, Airpush, TapJoy...) re-use device ID, but must its new Advertising ID. Therefore, update your RevMob to latest SDK should fix it.
Could you please share with me about tagging feature which needs to implement?