Outlook add-ins keeps getting disabled

We have an user's Content Manager add-in keeps getting disabled by Outlook. We have tried reenabling it in Outlook, but once you restarted Outlook it gets forced disabled by Outlook again with an alert saying it's disabled, and no Content Manager tab in Outlook. Has anyone encountered this kind of problem? 

I tried google searching for it and found some reference of Windows Registry key responsible for Outlook add-ins, and the one for Content Manager would shown as enabled on registry key even though it got disabled by Outlook. The M365 Outlook thick client and CM 10.0 client are both 64 bit installation.  Thanks!