Copy form elements feature

Hi,

There seems to be an issue with the copy feature in CF7. Whenever I try to copy a group of fields (like a container or Multi Field) it seems to just go dim as if it's doing work, but keeps dim for a very long time without making the copy. See screenshot below.



Is this a bug or could it be an issue from my end?

My PHP settings.

max_execution_time: 600
max_input_time: 600
memory_limit: 256M
post_max_size: 128M
upload_max_filesize: 128M

Any ideas?