Using Outlook 16 (365 Pro Plus) and Android built in gmail. If I create an entry on my phone, it shows up in Outlook on pc. If I make a change from my phone it changes in Outlook. But if I create the entry in Outlook and then modify it on my phone, it will not re-sync back to Outlook. As a matter of fact, even if I make it on my phone and then modify it in Outlook, any changes made from my phone will no longer sync it to Outlook. ONLY by creating it on my phone can I see the sync changes to Outlook.
I just switched from Windows phone to an Android, and I noticed this issue. If I use a Calendar app other than Outlook on the phone to edit an existing calendar event, it doesn't display correctly updated in Outlook on my PC or in the phone's Outlook App. Very annoying.