Image Preview in Structure-Field

For some reason I cannot display preview-images in a structure-field in the panel.

This is how it looks like:

The filename is shown instead of the image.

This is my blueprint (abstract):

images:
	label: Images
	type: structure
	fields:
	  file:
		label: File
		type: files
		query: page.images
		multiple: false
		uploads:
		  template: image
		required: true

I have played with some additional options for the file-field, but I cannot get it to display an image in the structure…

What am I missing?

Please post more context of the blueprint, the image should be shown next to the filename.

Thank you for the info that there should be an image.

… so I inspected my Kirby-Installation, and found a plugin which overwrote the preview (“k-files-field-preview”), … written by me (!) years ago.

Thank you