iMovie Crashes On Startup (High Sierra with eGPU)

When using an external eGPU, I am via the Sonnet Breakout box with and AMD Radeon 580, I have not found a way to use it with iMovie. iMovie loads and works fine with my 2017 MacBook Pro Retina lid open, but crashes immediately on launch if the lid is shut. I have the screens configured for mirror-mode.

Workaround: Leve the MacBook Pro lid open. In mirror-mode it really isn't a problem, just an inconvenience.