Originally Posted by
mustang7757 Very strange
Hey guys...I was having the same issue and realized something very simple was behind it (in my case at least). I tried everything else mentioned in this thread, but the issue was that background data was somehow switched off for Gmail.
Settings > Apps > Gmail > Mobile Data > Allow background data usage
I'm not sure how it got switched off for me, maybe accidentally in my pocket, but as soon as I toggled this setting, my emails popped up as notifications and I tested and verified new emails showing up as notifications instantly like they used to.