Hi William,
We’re having trouble reproing this on the release version of 4.19, so I’ve got a couple follow up questions. 
Can you repro this in a fresh project?
Are you using layers created during a preview build?
Also, if you are able to debug why you are getting a null pointer in GetChildHandle, that would help a ton. That section of code should just be tracing the struct holding the layer data, so it’s expected that it would return a handle even when you just added the node.
Thanks!
Lauren