Issue with IPv6 on Windows 10 client: 'Element not found'

[jmman]

* Server: Ubuntu with latest OpenVPN server (OpenVPN repo).
* Client: Windows 10, latest OpenVPN + TAP driver.
* Connection IPv4: works.
* Connection IPv6:issue:
```
Wed Mar 21 14:17:49 2018 ROUTE_GATEWAY 192.168.1.254/255.255.255.0 I=21 HWADDR=***
Wed Mar 21 14:17:49 2018 open_tun
Wed Mar 21 14:17:50 2018 TAP-WIN32 device [VPN] opened: \\.\Global\{***}.tap
Wed Mar 21 14:17:50 2018 TAP-Windows Driver Version 9.9
Wed Mar 21 14:17:50 2018 Notified TAP-Windows driver to set a DHCP IP/netmask of 10.8.0.6/255.255.255.252 on interface {***} [DHCP-serv: 10.8.0.5, lease-time: 31536000]
Wed Mar 21 14:17:50 2018 Successful ARP Flush on interface [27] {***}
Wed Mar 21 14:17:50 2018 do_ifconfig, tt->did_ifconfig_ipv6_setup=1
Wed Mar 21 14:17:50 2018 MANAGEMENT: >STATE:1521638270,ASSIGN_IP,,10.8.0.6,,,,,2001:***::2094
Wed Mar 21 14:17:50 2018 TUN: adding address failed using service: Element not found. [status=1168 if_index=27]
Wed Mar 21 14:17:50 2018 add_route_ipv6(2001:***::/64 -> 2001:***::2094 metric 0) dev VPN
Wed Mar 21 14:17:50 2018 ROUTE: route addition failed using service: Element not found. [status=1168 if_index=27]
Wed Mar 21 14:17:50 2018 IPv6 route addition via service failed
```
Any clues about how to fix this? Thanks!

[TinCanTech]

Windows "Element not found" can mean a lot of things ..

What IPv6 address are you trying to assign ?

Please see:
HOWTO: Request Help ! {2}