I've seen a similar Problem at customer site and here in my lab. Even after I got this in my logfile
2018-07-13 08:40:22,977 DEBUG [Match] OS match detected, MAC=00-1B-0C-96-AA-6A, IP=192.168.10.163, OS detected=Cisco IP Phone
2018-07-13 08:40:22,97...
