Handoff for Safari, Mail, Notes etc. only works for a few hours max. When I try to use it after my iMac has been on for more than a few hours it refuses to work. The strange thing is, the handoff-icon DOES appear in my Dock, but when I click it, nothing happens, and in when I try it with mail it says 'Handoff cannot be completed'. From my mac to my iPhone the same thing happens. A restart usually fixes it. Turning bluetooth/wifi on and off doesn't fix it, and logging in and out of iCloud...
Handoff only works temporary
Handoff only works temporary