Because the security of your data is our number-one priority, Salesforce is further enhancing the security of our APIs. If Salesforce detects suspicious API data-access behavior, we trigger automated actions in order to protect the account. In most cases, these actions include terminating user sessions and notifying the org admins via email. In more critical instances, when we detect extremely unusual behavior, these actions include freezing the user, revoking all access granted to them, and notifying the org admins via email. To resume after session termination, the user must log back in. To unfreeze a user, contact your Salesforce admin.
Where: This change applies to Lightning Experience and Salesforce Classic (not available in all orgs) in Enterprise, Performance, Unlimited, and Developer editions.