I was having a real nightmare getting Handoff and Continuity to work on my Mac Pro 4,1 Flashed to 5,1. I have an apple Wireless AC/Bluetooth 4 card in an adapter which appeared to be working fine. Handoff was showing as supported in System Report, but it just wasn't working. I tried all the turning handoff off and on, on my iPhone, Watch etc'. I removed and re-added all my stuff to iCloud. It was driving me crazy! Especially seeing as it was fine on my Mac Pro 3,1 at work ?!?!?!. When Sierra went Gold, I did a clean install, Still didn't work! Replaced the Wifi/BT card. It was joined to the same Wireless Ac network as all my other iThings. Eventually I disabled the Wired Ethernet and it started working instantly. Even setup unlock with Apple Watch. (yet to actually unlock successfully).