iCloud 4 vs. 6 digit security code

On MacOS Sierra, when attempting to enable sharing of my keychain via iCloud I get the following prompt:

Unfortunately, the only 2 factor iCloud security codes produced by my devices are 6 digits long. Clicking Forgot Code allows me to approve with other devices, but no notification appears on my other devices (iPhone, other MacBook Pro, older iPad Mini). Other iCloud services such as Messages, etc., are working on this device.

Anyone know how to get this code? Not having Keychain sharing (which was working before upgrading this laptop to Sierra) means many of the benefits of using a Apple with Keychain are drastically reduced.

Is is me, or did Apple totally drop the ball on 2 Factor security UX? Nobody who uses 2FA is happy, which is sad because this should be a major benefit of using all Apple devices.