You may face various Gmail issues because of the outdated Gmail app. If your Gmail not receiving emails on Android, several factors could be to blame for the problem. The first solution is to check that the email hasn't gone to another folder by mistake (like spam). Then check your storage level to see if you've run out of space. Your inbox settings might also be misconfigured. You can also reset Gmail for Android by clearing local data and enabling automatic sync. Also, re-sync your Gmail account and allow Gmail to work in the background. If that does not help, uninstall and re-install the Gmail app.
See also - Gmail not sending emails