Semantic-ui desn't work well when is imported in app.js

I have this pice of code: app.js

import '../../../semantic/dist/semantic';
require('./bootstrap');
import Toastr from 'vue-toastr';

Vue.component('vue-toastr', Toastr);
Vue.component('page-loader', require('./components/utils/page-loader.vue'));

const app = new Vue({
    el: '#app',
    mounted() {
        $('#loader').modal('show');
    },
});

When I choose to move semantic.js from base.html to app.js and build it as single app.js file I found some problem. When I did it method like $('#loader').modal('show'); work without console error but not at all. Modal will show at half of screen (not vertically centered) and without dimmer (body get proper class as modal is on but without dimmer action). Where did I mistake?