Return value from the promise .__zone_symbol__value

Ionic Framework ionic-v3
1

Hello, I have the following promise

getTimeOffSet(): Promise<any> {
    return new Promise(resolve => {
      firebase.database().ref('/.info/serverTimeOffset')
    .once('value')
    .then(data => {
      var offsetVal = data.val() || 0;
      var serverTime = Date.now() + offsetVal;
      console.log("DateNow: ", serverTime);
      resolve(serverTime);
    },  function (err) {
        err;
      });
      })
  }

and you are giving me back the following

t {__zone_symbol__state: null, __zone_symbol__value: Array(0)}
__zone_symbol__state
:
true
__zone_symbol__value
:
1517959915882
__proto__
:
Object

What can be wrong? I have time with that error I can not get anything from firebase with the functions