I am having a very similar issue…some featured images on my posts are not the correct size ever since the upgrade. I contacted my theme developer and they said it was an issue with the Jetpack Photon feature. I tried adding the Custom CSS above (since it sounded like the same issue I was having), but it didn’t work for me.
I will contact them now! Thank you.
I am having a similar issue. My featured images for each post on themangiamom.com is not spreading across like it used to. I believe it might be since the recent WordPress upgrade.
