Disappearing geometry when copying and pasting a curve

I have a problem that I have had a few times in Rhino 6.

I have a closed curve in a Rhino file, which when I copy and paste it using Ctrl+C and Ctrl+V, means that all of the geometry in the file disappears completely, including what I tried to paste. If I paste it into a new file it is fine.

I can’t post the file as it commercially sensitive, but I’d love to know if anyone else has come across this and know what might cause it.