Live Assist for Dynamics 365 will auto-disable agents who have not logged in during a set period. This is called the Auto-Disable Operator Policy. By default, this period is 90 days, but it changed to any number between 1 and 365.
If an agent does not log in for the specified period, that agent's account is disabled in the Engagement Portal. When this happens, the agent's privileges are revoked. However, the agent remains in the system and can be manually re-activated in the Engagement Portal.
If you wish to turn off this policy, please Contact Support.