No IP-Address from Zeroconf Plugin

I am using the native Zeroconf plugin like shown in the docs:

I am just getting the hostname, the IP-Address is always empty.

Has anyone had similar issues und can help me?

my code (ngOnInt -> this.platform.ready().then(() => {CALLED HERE}:

        this.zeroconf.watch('_http._tcp.', 'local.').subscribe(result => {
            if(result.service.ipv4Addresses[0] != null)
            {
                console.log("IP-Adress found: "+result.service.ipv4Addresses[0]);
            }

            if (result.action == 'added' || result.action == 'registered') {
                console.log('service added', result.service);

                var hostname = result.service.hostname; // --> found the correct hostname
                var ipAddress = result.service.ipv4Addresses[0]; // --> is empty
                

            } else {
                console.log('service removed', result.service);
            }
        });

my package.json:

{
    "name": "xyz",
    "private": true,
    "scripts": {
        "clean": "ionic-app-scripts clean",
        "build": "ionic-app-scripts build",
        "ionic:build": "ionic-app-scripts build",
        "ionic:serve": "ionic-app-scripts serve"
    },
    "config": {
        "ionic_copy": "./config/copy.config.js"
    },
    "dependencies": {
        "@angular/common": "2.3.0",
        "@angular/compiler": "2.3.0",
        "@angular/compiler-cli": "2.3.0",
        "@angular/core": "2.3.0",
        "@angular/forms": "2.3.0",
        "@angular/http": "2.3.0",
        "@angular/platform-browser": "2.3.0",
        "@angular/platform-browser-dynamic": "2.3.0",
        "@angular/platform-server": "2.3.0",
        "@ionic-native/core": "^3.5.0",
        "@ionic-native/file": "^4.20.0",
        "@ionic-native/zeroconf": "^3.10.3",
        "@ionic/lab": "^1.0.1",
        "@ionic/storage": "2.0.0",
        "cordova": "^8.0.0",
        "cordova-android": "6.2.3",
        "cordova-plugin-add-swift-support": "^2.0.2",
        "cordova-plugin-compat": "1.2.0",
        "cordova-plugin-console": "^1.1.0",
        "cordova-plugin-device": "^1.1.7",
        "cordova-plugin-file": "4.3.3",
        "cordova-plugin-splashscreen": "^4.1.0",
        "cordova-plugin-statusbar": "^2.4.3",
        "cordova-plugin-whitelist": "^1.3.4",
        "cordova-plugin-zeroconf": "^1.4.1",
        "cordova-sqlite-storage": "^2.6.0",
        "cors": "^2.8.4",
        "crypto-js": "^3.1.9-1",
        "font-awesome": "^4.7.0",
        "ionic-angular": "2.0.0",
        "ionic-native": "2.4.1",
        "ionic-plugin-keyboard": "^2.2.1",
        "ionicons": "3.0.0",
        "jquery": "^3.2.0",
        "multicast-dns": "^7.2.0",
        "ng2-charts": "^1.5.0",
        "rxjs": "5.0.1",
        "sw-toolbox": "3.4.0",
        "zone.js": "0.6.26"
    },
    "devDependencies": {
        "@ionic/app-scripts": "^3.1.11",
        "typescript": "2.4.0"
    },
    "cordovaPlugins": [
        "cordova-plugin-whitelist",
        "cordova-plugin-console",
        "cordova-plugin-statusbar",
        "cordova-plugin-device",
        "cordova-plugin-splashscreen",
        "cordova-plugin-zeroconf",
        "ionic-plugin-keyboard"
    ],
    "cordovaPlatforms": [],
    "description": "VoltoPlusApp: An Ionic project",
    "cordova": {
        "plugins": {
            "cordova-plugin-console": {},
            "cordova-plugin-device": {},
            "cordova-plugin-splashscreen": {},
            "cordova-plugin-statusbar": {},
            "cordova-plugin-whitelist": {},
            "cordova-sqlite-storage": {},
            "ionic-plugin-keyboard": {},
            "cordova-plugin-zeroconf": {},
            "cordova-plugin-file": {}
        },
        "platforms": [
            "android"
        ]
    }
}

my app.module.ts:

import {NgModule, ErrorHandler} from '@angular/core';
import {IonicApp, IonicModule, IonicErrorHandler} from 'ionic-angular';
import {VoltoPlusApp} from './app.component';
import {ConfigurationPage} from '../pages/configuration/configuration';
import {OverviewPage} from '../pages/overview/overview';
import {TabsPage} from '../pages/tabs/tabs';
import {AccountPage} from '../pages/account/account';
import {OutputPage} from '../pages/output/output';
import {LoginPage} from '../pages/login/login';
import {IonicStorageModule} from '@ionic/storage';
import {ChartsModule} from 'ng2-charts';
import 'chart.js';
import {MainService} from "./mainService";
import {Zeroconf} from '@ionic-native/zeroconf';
import {File} from '@ionic-native/file'
import {DatePipe} from '@angular/common';

@NgModule({
    declarations: [
        VoltoPlusApp,
        ConfigurationPage,
        OverviewPage,
        TabsPage,
        AccountPage,
        OutputPage,
        LoginPage
    ],
    imports: [
        IonicModule.forRoot(VoltoPlusApp, {
                backButtonText: ''
            }, {}
        ), ChartsModule,
        IonicStorageModule.forRoot()],
    bootstrap: [IonicApp],
    entryComponents: [
        VoltoPlusApp,
        ConfigurationPage,
        OverviewPage,
        TabsPage,
        AccountPage,
        OutputPage,
        LoginPage
    ],
    providers: [{provide: ErrorHandler, useClass: IonicErrorHandler}, 
        DatePipe,
        MainService,
        Zeroconf,
        File,
        mdns]
})
export class AppModule {
}