uploading Watermark picture is not working in Image Watermark

Hey folks,
got a little problem here.

I try to upload a picture as a watermark. I click on “Select Image” and than I choose the picture from my harddrive and upload it. afterwards it won’t be show up in the preview.

When I do it again but select it from my media library I get to the same result.

any ideas?

thanks!

https://www.ads-software.com/plugins/image-watermark/