Did the image sizes that you are missing exist when the image was originally uploaded?
I just did some testing. It is possible for a field to not return some image sizes, if the image size you’re looking for did not exist when the image was created. This is what I did.
I set up an image field, added an image to it. On the front end get_field returned the image array with all image sizes.
I then added an new image size. When I reloaded the page this new image size was not included in the image array. It did not exist when I originally uploaded the image.
I used plugin called AJAX Thumbnail Rebuild to rebuild the images. When I reloaded the page the new image size was included.
