Problems with plugin cordova when installing the plugin it is stopping the application.
cordova.plugins.diagnostic
well you didn’t provide that much details so I will just provide a wild guess.
Did you install or upgrade cordova.plugins.diagnostic to its version 4?
If so, have you read the CHANGELOG/README and did you had the new mandatory preference in your config.xml?
See “Specifying modules” chapter of the README https://github.com/dpa99c/cordova-diagnostic-plugin