Contacts saved by my app in iOS9 did not synchronise in iCloud.
They are visible in the Contacts app on the device I saved to, but were not duplicated to iCloud.com and other iOS devices.
The code hadn't changed since iOS6, and the same build worked on iOS8.
I placed the answer below, to help others.
I discovered that deleting the contact's image in the Contacts app caused synchronisation to resume.
I was saving my contact image in the PNG format, which breaks synchronisation in iOS9 for some reason, although it worked in all previous iOS versions.
The solution is to replace this with an image saved in JPG format.
NSData *imageData = UIImageJPEGRepresentation([UIImage imageNamed:@"IconR.png"],0.8);
ABPersonSetImageData(newRecord, (__bridge CFDataRef) imageData, nil);