Cannot copy node in CMS

I unpublished a document.
Clicked to copy it.
The document picker opened and I selected the folder to put it in.
I clicked OK.
The CMS was busy and then the popup disappeared.
However, the new document was not there.
It is on the docsite, so I can not get the logs.

I went to the console and tried it there.
I got a warning that the parent node was checked in.

I tried locally (so on localhost) on the same document. However, possibly different state of course.
It was OK.

I tried again on the docsite.
This time, an error message appeared: 'An error occurred, please retry'.

Berry said there would be a workaround:
Editing the document to be copied.
Then click done
Then do the copy

I tried it, but it did not work. The error message appeared and no copy was made.