Pretty much that.
If I leave my mac for a relatively short time, unlocking tends to work. However, if I've been gone more than 15 mins (the default for most macs to switch off the display and start power saving) then the auto-unlock doesn't work first time around.
Instead I get the message 'unlocking with apple watch' for a while with spinning timer and eventually it gives up and dumps me back at the password prompt. If I hit cancel the screen goes off again but hitting a key then re-starts the auto-unlock process which succeeds on the second attempt.
Makes the feature somewhat less than useful as quicker just to type a password! Hopefully a glitch that will get fixed at some point.
iMac (Retina 5K, 27-inch, Late 2014), macOS Sierra (10.12)
