When you install Outlook for Mac for Office 365, Outlook for Mac 2011 remains. Learn how to remove Outlook for Mac 2011 for the best experience:https://support.office.com/en-us/article/Running-Office-for-Mac-2011-side-by-side-with-Outlook-for-Mac-for-Office-365-dbea7d44-b212-4d8b-85bd-2722ca671c0f
For all of the known issues with Outlook for Mac, see https://support.office.com/en-us/article/Known-issues-in-Outlook-for-Mac-for-Office-365-af547e5c-4310-4d41-9944-08b1e842ebe4