Livereloading not working on real devices and emulator

when I try to run my app on a real device or an emulator I got these errors:

Failed to load resource: net::ERR_CONNECTION_REFUSED ion-dev.js?v=3.2.0:102

WebSocket connection to ‘ws://localhost:53703/’ failed: Error in connection establishment: net::ERR_CONNECTION_REFUSED

The app works but not the livereload feature.

Moreover I have no problems with:

ionic serve

Some informations about my system:

$ ionic info
[WARN] The pro_id field in ./ionic.config.json has been deprecated.

   Ionic Pro has been renamed to Ionic Appflow! We've copied the value in pro_id to id, but you may want to unset
   the deprecated property: ionic config unset pro_id


Ionic CLI : 5.0.0 (/home/user/.nvm/versions/node/v10.15.3/lib/node_modules/ionic)
Ionic Framework : ionic-angular 3.9.2
@ionic/app-scripts : 3.2.0


Cordova CLI : 9.0.0 (cordova-lib@9.0.1)
Cordova Platforms : android 8.0.0
Cordova Plugins : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 2.3.1, (and 15 other plugins)


cordova-res : not installed
native-run : 0.1.2


Android SDK Tools : 26.1.1 (/home/user/Android/Sdk/)
NodeJS : v10.15.3 (/home/user/.nvm/versions/node/v10.15.3/bin/node)
npm : 6.4.1
OS : Linux 4.18