I had a VERY similar experience. After update to the new 1.0 version private mail was working like a Charme but my companies address was not synchronized. Well, I received the push message about new mail from company, but they were not synchronized.
My setup is FP3+ with e/OS 1.x. I installed a couple of MS apps for my daily work. For mail I use Android-Outlook with 2 mail accounts (one is company, one is private mail). Also, my phone is managed through Microsoft Intune as Mobile Device Management System (company pushes it to the device).
So long story short: After deselecting ALL MS Apps from Advanced Security everything went back to work fine. A short double check (selecting only ONE MS App to be supervised by Advanced Security) the problem with no synchronizing. So to ME it looks like if your phone is managed from your company (at least MS Intune) it will interfere somehow with the Advanced Security.
Just my 2ct.