Handoff doesn't

Hand off doesn't hand off on my iDevices and iMac. All equipment meets the continuity requirements. The iMac is running HS 10.13.2 and all patches have been installed. iDevices are running iOS 11.2 and all patches have been installed. With Safari open on my iMac I get the Safari icon with the little computer in the upper right corner on the iDevice. I poke that and Safari launches. The address bar reports "Opening Webpage from Handoff". Eventually that ends and the tab reports "Loading". And there it sits. Oh, and the Handoff slider is green on the iDevices and on the iMac the "Allow Handoff between this Mac and your iCloud devices" is checked. All three machines are on the same WiFi.

So what is the magic to make handoff actually work?