linked contacts sync from ipad to iphone, but not to icloud or mac

Hi there

I am helping someone set up icloud and sync between their iphone, ipad and Mac. That all seemed to be working fine until we wanted to clean up her contacts - she has the same people in the address book multiple times with different names and information.

We used the link function on the ipad and that worked great. Data correctly changed on the iphone too so for example, 2 contacts become one with all the information intact

But not in icloud or the Mac. The two contacts stay in place as individuals. If I edit either of the two, the data goes to the icloud and the mac but the linked contacts never merge to the one selected

Can anyone suggest why this might be happening?

Thanks in advance!