Feature Image crop issue

Hello.

This is my website, http://theme-testing.eu
On the 3rd post you will see that the feature image is getting cropped.
I cannot find where to fix this and make it appear in the proper scale (16:9 is the desired one).
I also had to make a container for the video iframes as on the mobile version there were huge black stripes above and below them.
That put a huge gap under the feature image and now even if I use the right dimensions the gap is still there.

Thank you for your time.