Why ghost converts my images to png?

I can’t understand how responsive images work.
In the post editor, I’m creating the image gallery and some images become png.
This behavior has no sense for me.
I’m on 3.28
My ghost stack is here
Example post is here
Report is here

Hey there! Could you describe the exact method you’re using to add these images to Ghost? Step by step, what do you click, where does the image come from, etc