vagrant_1.8.5からvagrant_1.9.4にアップデートしたら下記のようなエラーががが

The provider 'hyperv' that was requested to back the machine
'default' is reporting that it isn't usable on this system. The
reason is shown below:

The Hyper-V provider requires that Vagrant be run with
administrative privileges. This is a limitation of Hyper-V itself.
Hyper-V requires administrative privileges for management
commands. Please restart your console with administrative
privileges and try again.

調べたらバグの模様
https://github.com/mitchellh/vagrant/issues/8527

対応方法はこちら↓
https://github.com/mitchellh/vagrant/pull/8548/commits/1dfc646fb3dd0f7b22a45d6c17ae0669933d7011