Ionic + Firebase + Websocket ERROR

#1

When I upload a certain amount of data to the Firebase database, I get the following error:

WebSocket connection to ... failed: Failed to send WebSocket frame.
Firebase Database (4.1.3) INTERNAL ASSERT FAILED: sendRequest call when we re not connected not allowed.

Eventually, the data is sent to firebase, but after 20 seconds instead of 1 second.
The error only seems to happen on iOS.

Anyone have any idea/solution about this issue?

ionic info

global packages:

    @ionic/cli-utils : 1.5.0
    Cordova CLI      : 7.0.1 
    Ionic CLI        : 3.5.0

local packages:

    @ionic/app-scripts              : 2.0.2
    @ionic/cli-plugin-cordova       : 1.4.1
    @ionic/cli-plugin-ionic-angular : 1.3.2
    Cordova Platforms               : android 6.2.3 ios 4.4.0
    Ionic Framework                 : ionic-angular 3.5.3

System:

    Node       : v6.11.0
    OS         : macOS Sierra
    Xcode      : Xcode 8.3.3 Build version 8E3004b 
    ios-deploy : 1.9.1 
    ios-sim    : 5.1.0 
    npm        : 5.3.0