There's an update to the jessie distribution (sometime in the last week) that changes the bluetooth mac address on pi3's / pi zero w's to 43:43:A1:12:1F:AC.
This upsets piBeacon no end if it's applied to > 1 pi, since they know have the same bluetooth mac address.
See https://github.com/raspberrypi/firmware/issues/860.
I've just fixed on of my pi zero w's by reverting to a disk image I (luckily) made a week ago.
Looking at how to fix by deinstalling/installing an older set of packages, but haven't cracked it yet.