Just want to make sure that I understand.
You have a gallery field on a post. You open this to add to the gallery.
When selecting the gallery image there is different field that is available while selecting the gallery image to select another image.
All I can do is confirm that what you are seeing is the same thing that happens for me and tell you to submit a bug report here https://www.advancedcustomfields.com/contact/, it might be looked at faster
