In one of the default views of KYOcount viewer we have a collumn called "Hostname". In that collumn I can see some, but not all host names. Why?

Device-discovery will iterate through IP-adresses and for each found machine it reads the hostname (or SMNP sysName) but stores it only if this name is really resolvable AND it resolves to the right IP-adress. If not (it is possible that devices have nonsense hostnames configured or that the network doesn´t have a name service at all), then KYOcount avoids using those (invalid) hostnames by simply not saving them. Because if hostnames are stored, KYOcount tries with first priority to use this hostnames for the collection of counters.

Maybe this means the devices in your viewer, which appears without hostname, their hostname could either not been resolved or it led to another IP-adress during the discovery. This could happen if, for instance, a DNS was not up to date at this time.