React-native Firebase database.Ref.on fires only once

I'm developing on an Android, connected device (not emulator), with Live Reload enabled. Each time I make save a file, it reloads my app on the device - which is what I want.

I'm currently using Firebase for Auth and Realtime-Database. To retrieve the logged user datas, I have a Redux action that calls the firebase.database() like this:

// AppRedux.js
const reducer = (state = initialState, action) => {
    switch (action.type) {
        case 'setCurrentUser':
            return { ...state, currentUser: action.value }
            break;
        // { ... }
    }
}

const store = createStore(reducer, applyMiddleware(thunkMiddleware))
export { store }

const setCurrentUser = (user) => {
    return {
        type: "setCurrentUser",
        value: user
    }
}

const watchUserData = () => {
    return function(dispatch) {
        const { currentUser } = firebase.auth()

        if (currentUser) {
            console.log(currentUser.uid) // I always have the right uid, so firebase.auth() always works
            const ref = firebase.database().ref('users/' + currentUser.uid)

            ref.on('value', (snapshot) => {
                const user = snapshot.val()
                console.log(user) // I get there onlye once !

                dispatch(setCurrentUser(user))
            }, (error) => {
                console.log(error)
            })
        }
    }
}
export { setCurrentUser, watchUserData }

And here is where I call this action:

// Main.js

// { ... other imports}
import { watchUserData } from '../redux/AppRedux'


const mapStateToProps = (state) => {
    return {
        currentUser: state.currentUser
    }
}
const mapDispatchToProps = (dispatch) => {
    return {
        watchUserData: () => dispatch(watchUserData())
    }
}

class Main extends React.Component {
    constructor(props) {
        super(props)
    }

    componentWillMount() {
        this.props.watchUserData()
    }

    render() {
        const { currentUser } = this.props

        return (
            <View>
                <Text>Hello { currentUser && currentUser.firstname }!</Text>
            </View>
        )
    }
}
export default connect(mapStateToProps, mapDispatchToProps)(Main)

This piece of code works perfectly - but only once. When Live Reload fires, it won't work anymore.

Note that firebase.auth() still works and gives me the right uid, but firebase.database().ref('users/' + currentUser.uid).on('value') won't fire anymore

I have to npm run android (which is equal to react-native run-android) for it to fire again.. until the next Live Reload.

Note that it doesn't work even if I logout and signin again. I still have to npm run android for it to works.

Here is my package.json in case it would matter

"dependencies": {
    "react": "^16.3.2",
    "react-native": "^0.55.3",
    "react-native-firebase": "^4.3.6",
    "react-native-google-signin": "^1.0.0-rc5",
    "react-navigation": "^2.14.2",
    "react-redux": "^5.0.7",
    "redux": "^4.0.0",
    "redux-thunk": "^2.3.0"
}

Is there something I'm doing wrong? Is it because I have a free Firebase plan, and I make too much calls or something?