Pictures not showing up in Picture gallery

[Spirit of Eden]

Hello to the Forum,

I´m asking for help with a problem with the Picture gallery. Since I am a passionate astrophotographer (and a weather enthusiast too, of course) I wanted to set up a picture gallery to show my astro images on my website.

After installing the plugin, I left the "edit settings" by default. Then I uploaded some photos which went well. Thereafter update menu. In the album, there are still two "empty images" and the uploaded ones. Furthermore, I cannot select one picture to show it in its full resolution. I tried .jpg and .png. My browser is Safari, also tried Tor-browser.
Please see the attached screenshots to show what I mean. It would be great if someone has a solution to this.

Thank you in advance and greetings to all weather enthusiasts.
Stefan