IDeckLinkOutput::DisableVideoOutput crashes

I'm running a Mac app against SDK 9.7.1/Driver 10.4 connected to an Ultrastudio4k. I have some code that calls IDeckLinkOutput::EnableVideoOutput() to see if another app is attached to the box which returns "access denied" in case its already in use. In this scenario it works just fine. Following this latter call, DisableVideoOutput() is called. This latter crashes if prior to start the app I have "unplugged" and then "plugged back" the thunderbolt connection to the box. Is anybody have experienced this, or is there another way to detect that the driver is healthy.