Hey there @Sven_Kalwach and welcome to the Community 
I have to say that our app, indeed, has a limit for the number of reviews displayed. The widget only captures the 100 latest reviews. After that, the filter you’ve chosen is applied to these reviews, which is why you see only 80 reviews at the moment.
I do understand your point that it might work not as expected, and deeply apologize for all the frustration caused by this 
We totally agree that it would be amazing to display all the reviews in the widget. I’ve added your idea to the Wishlist and we’ll try our best to consider it in our future updates. You can keep an eye on it here - Display all reviews in the widget (remove 100 reviews limit)