Hi John!
If you run the regenerate thumbnails plugin: https://wordpress.org/plugins/regenerate-thumbnails/ it should turn featured images into the same size.
If this doesn’t work, try installing and activating this plugin: https://wordpress.org/plugins/alx-extensions/ and then run the regen thumbs plugin. Alx Extensions plugin upscales featured images that are too small and then crops them, so small images don’t have a strange size.
