I checked the header and footer.
There are no objects present in either and the selection pane also does not display any.

I figured that the two greyed-out objects shown in the picture above will vanish if I select and delete "Abbildung 4". Oddly enough though, now there are four of these greyed-out objects.

On another page with two figures and one greyed-out object, the object will vanish if I delete any of the two figures.