Answer
Have the affected user log into the Aurena web client via Azure AD at least once first, before trying the CRM Panel Outlook Add-In. The very first time any user authenticates to Aurena via Azure AD, a one-time secondary confirmation prompt appears (confirming access to the specific App ID) — the CRM Panel Outlook Add-In has no built-in handling for that extra prompt, so if a user has never completed it via the full Aurena web client first, the Add-In's own login attempt silently loops back to its login screen instead. Completing that one-time confirmation via a normal Aurena web login first resolves the Add-In's login loop.