After updating to version 9.1.2109 (99b7b93) both of my Windows 10 machines started throwing this error for my outlook.com email:
An error occurred
[Exchange Web Services] Set action is invalid for property.
That’s all I get.
Other than the error, it seems to send/retrieve messages just fine. But it’s definitely the new client because I updated one machine immediately and waited several days before udpating my laptop and the laptop never had the error until I updated.