On my site, gathforblueash.com, some blog feature images resize for mobile, others don’t.  I imagine there must have been a difference in how I uploaded them but I can’t figure out the trick.  The images in the media file are the same dimensions.
Not working: the picture for “Blue Ash Council Moves Towards Legalizing “Golf Carts” on Roads…
 
working: Kenwood and cooper development presentation shared