Just did some testing, i deleted the child devices where isComponent is true on 1 device and false on another. The ones with children containing isComponent: true continue to fail state retrieval. isComponent:false child components retrieve state and work with alexa.
Update:
Pass isComponent:false to addChildDevice would probably do the same without the need for an additional smartapp and keep the child device associated with the parent. This creates the virtual child device which can be invoked from the parent. I verified the child device is visible in alexa (for me it was a motion sensor). I couldnt verify google assistant, but other the parent devices started working which is a very good sign.