Looks like one of 2 things. Either Apple is having some problems with their server that handles push data or 9.3.1 has a bug which causes push and or notifications to be slow or at times not come through at all. I started noticing this problem on my brand new iPad Pro 9.7 on Saturday and my iPhone 6 yesterday evening. This problem exists with the mail app(Yahoo mail, Exchange(Microsoft), and Apple iCloud) as well as several other apps such as Facebook. Notifications sometimes never come through until I open the app itself. I'm running 9.3.1 on both and restored the iPad to new through iTunes yesterday. Yes I have made sure all email accounts are set to push. Fetch is set to manual for all other items. No improvements today and I've been on cellular as well as my home wifi and work wifi. Anyone having issues?