1. Install CustomDevice sample.
2. Create an instance of the custom device using the Tools menu
3. Trigger a domain reload via a script change
4. Observe errors in console

Bit of a conundrum. Problem is that we trigger an initial update during system initialization through InputSystem.RunInitialUpdate. We do this so that MonoBehaviour.Start methods have devices available to them.

However, when system initialization is triggered by one specific third-party InputSystem.RegisterXXX call and there's another InputSystem.RegisterLayout call waiting, then any device depending on the RegisterLayout call will cause an error as the layout is not yet available.