illogical behavior – image opens twice

Hello,

I have installed it, activated it and click in a page on picture that is linked to its media file. After clicking on that picture, the destination media file (image) gets opened and a layer of that same image is layed over it and you have to close two pictures when viewing only one…
If I give the image no link to media file, there is no lightbox coming up.

The behavior is the same with Chrome and Firefox on desktop.

Please check here:
http://danceandsoul.de/stundenplan/

Additional installed image related plugins are:
https://ww.wp.xz.cn/plugins/slideshow-jquery-image-gallery/
https://ww.wp.xz.cn/plugins/wp-google-map-plugin/