When logging out and back into a Windows device, the Signature 365 Outlook add-in is removed. Waiting a short period and closing and reopening Outlook causes the add-in to load correctly.
This behaviour is usually seen on RDS / Citrix servers, or devices / domains utilizing roaming profiles.
Ensure that the following folder and its contents are not being removed when the user logs off the device:
When the contents of this folder are removed, Outlook must determine that the add-in is required, download the add-in data from Microsoft servers, and then install the add-in and display the menu button.
The resulting delay prevents the add-in from loading until completed and requires restarting Outlook.