Do you have any Bluetooth devices connected to you Mac? I was having the same issues with the unlock feature, then I noticed the Bluetooth symbol in the menu bar was showing it was paired (three dots through the center of the symbol) even though I had nothing paired with my laptop. I opened Bluetooth preferences and deleted the two devices listed there that had been previously connected, but were not currently connected. After deleting these items, the Bluetooth symbol returned to its normal unpaired look, and the unlock feature started working 100%.
I then tried experimenting a little. First, I paired my Bose speaker. 100% failure, required my password every time. Next, I unpaired the speaker and paired an Apple Magic mouse. This resulted in about a 50% failure rate but always worked when I clicked cancel then tried logging back in. I have not tried any other devices or multiple like a mouse and keyboard.