As it is stated here https://firebase.google.com/docs/cloud-messaging/js/first-message#monitor-token-refresh FCM tokens can be refreshed in some cases but I don't see anything that deals with it in phonegap push plugin documentation. Does someone know how is it solved in this plugin?
Answer I got from phonegap github: https://github.com/phonegap/phonegap-plugin-push/issues/2415 which states:
The on('registration') event is fired if there is a token refresh. Each time you get a registration event you need to check to see if the value is different than the one you previously had. If so, send it to the server.