To force and add-in to always stay enabled, create the following registry value:

KEY: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Resiliency\AddinList

NAME: ProgID of the add-in

VALUE: 1

To find the ProgID for an add-in, look in the registry here: HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Outlook\Addins Every subkey of one of the above keys is named with a ProgID of the corresponding add-in.

If you require more detailed technical information, you will find it in this Microsoft article.