Update: The next_image_link and previous_image_link retrieve the neighbouring Post in the WP database. The next_image_link just looks for the next item in the database (which is usually based on upload date/time).
It look’s like we may have to create a new function to solve this problem:
Maybe an Array of ID’s for each ACF Gallery which can be navigated on the attachment.php?
Any help greatly appreciated :D!!
