To be honest, I don’t know why your code is not working. Copying images from one blog to another is not something I have any experience with.
And the difficulty with updating acf values to point to new images, when you’re dealing with unknowns like repeaters and flex fields, well, I don’t thing that there’s any real way to do this dynamically, especially by using get_post_meta() to get the values.
The best way that I can thing of would be to work through ACF using the ACF function to get values and use get_field_object() https://www.advancedcustomfields.com/resources/get_field_object/, then do whatever you need to do with the images to transfer them. After getting all the values this way and moving the images you can then use update_field to update the values of the post where you’re copying to. https://www.advancedcustomfields.com/resources/update_field/.
