iPhone 6s, iOS 9.3.2
On my iPhone, mobile-mail is scheduled to fetch emails from my Gmail account every 15 minutes.
I recently noticed that more than 15 minutes can pass - the longest so far was 24 hours - without mobile-mail updating my email inbox.
I had mobile network and WIFI connectivity during those 24 hours. I have accessed the internet, used iMessage and WhatsApp, and updated apps.
When I opened mobile-mail, it connected to Gmail and - to my surprise - downloaded 24 hours of emails. Before doing so, I could see that the notice at the bottom of the screen said that my inbox had last been updated the day before.
How do I figure out which setting is preventing mobile-mail from fetching my Gmail according to the set schedule?