Some android users have been suffering from delayed or inexistent notifications since November. The issue mostly affects Gmail on Nexus devices running Marshmallow (but other apps, devices, and Android builds have also been reported). Two weeks ago, Gmail 5.10 rolled out but the updated app only fixed synchronization for Hotmail accounts, not other types and most importantly, not Gmail accounts. At the time, we knew that the more pervasive sync bug had been identified by the team, but that the fix hadn't been implemented yet.
It seems that the woes of everyone suffering from this issue are about to be over. The corresponding AOSP issue tracker item has been marked as "Future Release," and Googler Orrin stated on the Nexus Help Forums:
Hey Everyone,
Thanks again for your patience on this while the team investigated the issue. I’m happy to announce that a fix has started to roll out. This fix requires no action, and will roll out globally over the next week.
Please let us know about your experience as this fix is rolling out.
When members started thinking that the February security fixes that were rolling out to Nexuses included their problem's fix, Orrin further explained:
For some additional clarification, the fix will not come through a system update, hence there is no OTA file or anything like that. I know this isn't ideal for everyone, but the best indicator of when you receive the update is to notice that the issue itself has been resolved.
Please continue to report back on this thread over the next few days/week.
So it seems like all you can do is sit tight and wait for the fix to be magically triggered somewhere for your account. Burning incense could get you closer to the front of the waiting line, but only if you believe in such voodoo. When the rollout is final, it'll hopefully be the end of this saga altogether.
Thanks: Michael Oghia