We are experiencing the same issue. It seems there are several problems with the Google VR plugin with the latest versions of Unreal.
The only way we were able to get it to work was by doing this: GoogleVR - Crash opening application on device. - VR and AR Development - Unreal Engine Forums
Currently we actually develop in 4.19 and then use the github branch of 4.20.2-googlevr to build and package the project for release.