The NTP client on the HPDU follows the NTP RFC and so the HPDU rejects any NTP servers whose root dispersion is more than one second. An NTP server with a dispersion of more than one second is considered an inaccurate NTP server by the HPDU. For information on NTP RFC, visit https://tools.ietf.org/html/rfc4330.
Windows NTP servers might have a root dispersion of more than one second, and therefore cannot synchronize with the HPDU. When the NTP synchronization issue occurs, change the dispersion settings to resolve it.