The patch update to Office 2016 / 365 which started distributing in early September 2018 has a flaw. As a result the Outlook AddIn pane can become detached from the reading pane in Outlook, appearing as a separate window on the desktop with a title 'AdxTaskPane'. This issue affects many AddIns, not just that from Legrand CRM, but impacts only Office 2016 / 365 - earlier releases of Microsoft Office are unaffected. It has been acknowledged as a fault by Microsoft and will (presumably) be corrected in a subsequent patch release.
In the meantime the following workaround will prevent this behaviour from occurring:
Open the Outlook Application and navigate to File > Options > General > User Interface options
Select Optimize for compatibility (application restart required)
See https://answers.microsoft.com/en-us/msoffice/forum/msoffice_outlook-mso_win10-mso_o365b/adxtaskpane-appering-in-outlook-for-all-the-addins/94b08de5-f6ee-421f-a45f-ee5557141ce8 and https://www.risual.com/2018/04/12/azure-information-protection-toolbar-issues-adxtaskpane/ for more information.