Featured image not resizing

are you selecting an image that was already uploaded? Imsanity kicks it at the time you upload the image. so if you choose an image that was uploaded previously and is already in the library, Imsanity won’t kick in at that point and resize it.

I just tested uploading a featured image and imsanity does resize it using the size limit specified for “Images uploaded within a Page/Post” in Imsanity settings.