Hi Helmet,
As you said you have been facing this issue since some weeks so can you confirm that you have done any Office 365 Service upgrade which affect Mac set up for Office 365.
Can you please update the Outlook 2011 with latest automatically or manually?
You can do this with
To be compatible with Office 365, make sure that you have the latest updates for Office for Mac 2011.
- Open an Office application (for example, Microsoft Word for Mac 2011).
- On the Help menu, click Check for Updates.
- Choose automatic or manual updates.
For more information, see Set up your Mac for Office 365
Thanks,
Pratik Pandya