I wanted to tell, that I have the same problem with updating changed images as told above. Currently I am using spine 2.1.27 pro.
I have a freshly created, but already one time saved and even reloaded project, one skeleton set up with images, still no animation.
If I edit the image in the images-folder, nothing changes within spine. Even not, if I temporarly change the images folder and then set it back: still the old images appear again. Then I renamed an edited image, "hand_front" to: "hand_front_new". In the attachment under the bones slot is still "hand_front" =the old name given, while in the skeleton a red box "missing" appeared around the assigned bone. Now I rename the image in its folder from "hand_front_new" again back to "hand_front". Now the red box changed to green with the text "loading" - but nothing else happens.
I have to shut down spine and start it again and load my project therefore the second time=NOW the correct edited image is displayed in the skeleton, and spine updates also furtherly if I now continue to edit images.
So it seems it is a problem, if a project was created for the first time and before spine at least one time was closed and restarted, already here images after setting as attachment are edited and have to be updated .