A particularly aggravating issue happens to be plaguing a number of Gmail users on Android as of late. Affected people report a complete loss of the ability to sync their accounts, both manually and automatically. The cause is still unknown, but users report experiencing it following the 4.8 update. Yet clearing updates and returning back to a previous version doesn't fix the problem, suggesting some other source is to blame.
Google is looking into the matter. A recent response on the issue's Google Groups page says that the company has moved past reproducing the error and is now testing solutions.
If you're experiencing this bug, this isn't yet the good news you were expecting. But it's a step in the right direction. Stay tuned for more information when the good news comes, though you will more likely be alerted when those Gmail notifications start appearing again.