Chat App Angular Ionic Read Messages Problem

I want to show a badge, if the actual user has a unread message. It works if the first user write a message to the second user. But if the second user writes a message in the same time to the other user the badge comes but it is only two seconds.

The messageRead Function is triggert in the toDetail Function, which is a function if the user tabs on the Chat.

async MessageIsRead(uid: any){
    const db = getFirestore();
    const messagesColRef = collection(db, "messages");
    const currentUserUid = (await this.fireAuth.currentUser)?.uid;
    onSnapshot(messagesColRef, async (messagesSnap) => {
      const messages = =>;
      for (const message of messages) {
        if (message['from'] == uid ||  message['from'] == currentUserUid) {
          const messageRef = this.firestore.doc(`messages/${message['id']}`);
          await messageRef.update({ read: true });
        }else {

To show the Badge on the User I have following code:

 this.items = any) => {
            const conversationMessages = filteredMessages.filter((message) => message['from'] === user.uid );
            this.unreadCount = conversationMessages.reduce((acc, message) => {
              if (!message['read']) {
                const isUnread = conversationMessages.every(otherMessage => {
                  if (message['createdAt'] < otherMessage['createdAt']) {
                    return false;
                  return true;
                if (isUnread) {
              return acc;
            }, 0);
            return {
              name: user['name'],
              image: user['image'],
              uid: user['uid'],
              read: this.unreadCount > 0 
    } catch (error) {

And then the HTML:

<ion-badge color="danger" *ngIf="">&nbsp;</ion-badge>

How can I make it, that the badge is only shown if the other user tabs on the chat?

The whole code is on Github: GitHub - mark-baumann/drink-together

My database:

Data Table 1 Datatable 2

I expected it would only show the badge if the actual user tabs on the chat and it won´t be gone after seconds.