When I logged into iCloud today and checked my contacts I find that some of the groups are blank, yet on my iMac all the contacts are there for both iCloud and on my iMac. Can anyone suggest how I can rectify this
On the iMac, in the left column of the Contacts app there's a heading "iCloud" and another "On My Mac" (assuming you have contacts stored in both locations). If a group is under the On My Mac heading, it will not appear in iCloud.