'Attachments' is not available as an option for 'Fields to copy' for a clone and link post function. At first, I couldn't reproduce this bug, but then 'Attachments' disappeared as an option and I'm not sure what changed.
One thing that I did before this occurred is edit the description of 'Attachment' from the Field configurations page, but I'm not sure if that could have actually affected this.
This is also happening with the create subtask post function.
Use the additional actions field to clone attachments from one issue to another. The script, to clone all the attachments will be