I'm having the same issue. I just got the Pixel 3 weeks ago, switching from Blackberry, and my email notifications can take anywhere from 5 mins to 3 hrs. If I open and refresh my email account, they'll come through, but I don't want to keep checking my phone every 5 seconds. That's what notifications are for. I've been using my old BB on my wi-fi to alert me when emails are coming in at home, but that doesn't do me much good away from home. I've tried the suggestions in this post to see if my settings needed to be changed, but everything seems up to snuff. Not sure what to do. It's annoying...