Problem with importing images

I’ve set up the whole synchronization.
Process lasted very long (products) but on wordpress side, it had finished.

But when I enter shopify, only few of more than 220 products has images.
When I enter particular product there is error message with message: Image: File extension does not match file format.

I’m attaching screenshot (in polish).
What is wrong with this? What am I doing wrong?

The problem is critical and weighs the fate of the entire integration and creation of the store on Shopify.