With the roll out of IPv6 we are met still with bugs and challenges. One we have stumbled across is that when you configure a static IPv6 address you still receive a DHCPP as well. It would seem Microsoft have a bug that when you enable a static IP it doesn't turn off the DHCP function.
To fix this is more simple than you may think.
Open Powershell as an Administrator and run
Set-NetIPInterface "EthName" -AddressFamily IPv6 -DHCP Disabled
This turns off the DHCP function but allows your statically assigned IP to work.