you are right, it was not clear. I did the same action on a file that did not go through icloud, and things were fine. I tried it with two different files.
To make it clear, here are the flows
A on Mac -> duplicate to C -> save it on icloud -> look at it, change some value on iPad -> edit it on Mac with copy paste -> fail
A on Mac -> duplicate to M -> edit on Mac with copy paste -> works
I duly update systems and apps every time I am notified both on Mac and on my iPad Mini.
There are differences in the two Numbers apps, but I can't say what your trouble may be. I have created documents in the iOS version and edited on the Mac, and reopened on the iOS device, and vice versa without difficulty.
My documents did not include any web clippings, which are a big unknown here.