Why values from event data are not assigned to the vars of the component?

Hello,
In vue/cli 4 app I have a component and in mounted event when onPageChanged event is triggered I read data from
from this event and assign then to the vars of the component site_name, site_heading…
In the console of the app I see that these values from data are not assigned to the vats of the component…

<template>

    <section :class="'column_content_centered listing_header_' + parent_component_key" class="m-2 p-2" style="border: 3px dotted red !important;">

        site_name::{{ site_name}}
        <h1>:{{ site_name}}; </h1>
        <h2>:{{ site_heading}};</h2>
        ...

    </section>

</template>

<script>

    import {bus} from '../main'
    import appMixin from '@/appMixin'

    export default {
        mixins: [appMixin],

        data: function () {
            return {
                site_name: '-==',
                site_heading: '++--',
                site_description: '---',
                is_admin_page: false,
            }
        }, // data: function () {

        props: {
            message: {
                type: String,
                required: false,
                default: ''
            },
            ...

        }, // props: {

        methods: {

            triggerListingHeaderRightButtonClickedEvent() {
                bus.$emit('listingHeaderRightButtonClickedEvent', this.parent_component_key)
            }

        }, //methods: {


        mounted() {

            // let self = this
            bus.$on('onPageChanged', (data) => {
                console.log('onPageChanged data::')
                console.log(data)
                this.site_heading = data.site_heading

                this.site_name = data.site_name
                console.log('!!! this.site_name::')
                console.log(this.site_name)  // It show s valid values from fata

               this.site_description = data.site_description

                this.copyright_text = data.copyright_text
            })
        }, // mounted() {

        beforeDestroy() {
            bus.$off('onPageChanged')
        },

        computed: {

            right_icon_class() {
                return this.right_icon + ' a_link p-1'
            },

        }, // computed: {


    }
</script>

What is wrong ?

Thanks!