Gmail app not syncing automatically

[Truepeace]

Hi,
I have done my research before posting this thread, and I've seen many other similar posts but none of them helped.
The Gmail app is not syncing automatically so it is not receiving new emails unless I enter the app and swipe down to refresh, or if I turn off and on "Auto-sync data". Things I tried:
I checked that "Auto-sync data" is turned on in my settings and that Gmail sync is checked in my Google account sync settings.
I cleared all the google apps cache (google play services, framework, email, gmail).
I disabled the stock Gmail app then enabled it and updated it.
I force uninstalled Gmail (since my phone is rooted) and reinstalled again from the Play Store.
I rebooted into recovery and cleared cache and dalvik cache.
I removed my Google account and re added it.
I included the Gmail app in "Ignore battery optimizations" in the battery settings, the google play services are included by default and my phone is not in power saving mode.
I checked Gmail app settings, my email address settings, "Notifications" is checked, "Data usage" ->"Sync Gmail" is ticked, "Manage labels" -> Primary sync is on on the last 30 days, "Inbox sound & vibrate" -> "Notify for every message" is unchecked by default but I checked it.
Using LG G3 on Marshmallow 6.0 stock rooted.

 

[Rukbat]

Turn the auto sync interval to off - that sets it to "push" - you get emails as the server gets them. (And try a different email app - the GMail app has different problems with every update.)

 

[Truepeace]

I got your point on the "push" thing but I didn't try it since I made it work. And yeah my friend who got the same problem is using a 3rd party app.
I just re did what I mentioned in my initial post but all at the same time, I turned off Auto-sync, removed my Google account, cleared Gmail, Google Play services, Play store, Google services framework and Email cache, rebooted into recovery, wiped cache and dalvik cache, added back my google account, turned on auto sync and it worked. So nothing new, I tried them all before but not successively, but I am sure it's not my phone's problem and it's a bug in Google's apps or Gmail since a lot of other users have faced the same problem which is unfortunate.

 

[TheNeckerCube]

Just wanted to confirm I'm having this same problem but on another phone.