One reason for this problem can be the disabled IMAP. IMAP is the technology that Gmail uses to deliver the emails to your device, which may be disabled on your iPhone causing Gmail won't load on iPhone issue. Open Gmail on a browser and open its settings. In the settings, you will find the Forwarding and IMAP/POP tab –click on it and enable the IMAP under this tab. This should solve your problem with Gmail and iPhone.

Visit: Gmail notification not working

There could be multiple reasons why you encounter the issue- Gmail notification not working. Irrespective of the device you use, the common reasons are system bug or that the notifications might be disabled in your mobile app.