frequently Visited websites sync

hi, i've got an ipad/IPhone and IMac with MacOS Sierra installed and all iOS devices updated to latest software but frequently visited website sync between iMac/iPad and iPhone not syncing properly on Safari. How do I turn this feature off and back on again across all my iOS devices and MacOS Sierra on Safari ? I've tried seach the internet but the tutorials and all based on older versions of iOS and OSX.

thanks in advance