If your MeisterTask app is missing some work or showing outdated data, it may not be synchronizing properly with the web app. To solve this issue, you can trigger a manual sync directly from the mobile app.
To trigger a manual sync on the iOS app, read this.
To trigger a manual sync on the Android app, read this.
When you open the app, it may take a few minutes to sync, so don't worry that your data is lost.