Hey,
Hope you are doing well. I am facing an issue with all the home page sliders. Firstly, their thumbnails are missing however all the media files have been uploaded successfully in the media section. 
There are some other pages too where thumbnails are missing. 
2ndly, I can't find a way to edit the background images of the sliders. 
Please help me out from this.

Thank you. 

are you there?

Please see the attachments. This is what is showing when I import the demo data.