My Outlook 365 has been acting up, refusing to start up without a reboot. Some internet research lead me to the solution: My outlook.pst file was corrupted and needed to be repaired.
If you have this problem, I’ll let you know what fixed it for me:
Go to the “Program files” folder on your computer and search for “scanpst.exe”
Open scanpst.exe it and locate your outlook folder. It is probably hidden, so you will need to “Show hidden files and folders.”
Run the scan on your Outlook data (pst) file and repair any errors.
Should work like a charm!