I have a MacBook Pro running OS Sierra 10.12.1 and one external monitor. I have a Plugable UD-3900 docking station connected to my MacBook Pro and ext. monitor using HDMI connection. After upgrading to Sierra 10.12.1 yesterday, my external display is freezing intermittently and I’m having to reboot the docking station to fix. Are there any updates for this issue or is there a work around?