A quick fix for missing Gmail notifications on Android phones
I occasionally stop getting Gmail notifications on my Google Pixel 2XL android phone. I later find that I have a whole bunch of emails that I had missed. I am not sure what causes it however I have found a way to make it work again.
Under Settings, select Accounts and then your Google account. Once opened click on Account sync. You will be able to see when it was last synced and you will probably find that it failed a while ago. You can either turn the sync on and off to force it to sync again or select the Sync now option on the three button menu in the top corner to sync all the services.