If you are dealing with the issue of Gmail notifications not working then you can try Gmail in another web browser. It is the simplest hack available to deal with the issue. If you are using Chrome, then start by opening Gmail in Firefox and see if it is working properly or not. If it is working properly, then you need to figure out why it is not working properly in Chrome. Likewise, if it is not working in the mobile application then you need to start by switching the browser and see whether you are having better experience or not.