OK, So I have tried this (found it in this forum) and added this css code to input.css
.acf-image-uploader .view {
width: 150px;
height: 150px;
background-color: #dddddd;
It works for now but it does not look pretty. So I am still looking for another solution.
I still cannot find the anwser to this bug or problem or … I surely could use some help since the site is live!