We have confirmed with Microsoft a bug in Entra ID (Azure AD) SSO Auto-Provisioning, where an update of any user attribute also updates the user's Allocated Storage (a.k.a. space_amount) to Unlimited (a.k.a. a very high number). Since Microsoft offers the integration as an Enterprise Application, they need to fix this.

In the meantime, Box should document the situation, do whatever they can to offer a workaround, and assist Microsoft to expedite the fix.

(See also https://learn.microsoft.com/en-us/entra/identity/saas-apps/box-tutorial & https://learn.microsoft.com/en-us/entra/identity/saas-apps/box-userprovisioning-tutorial for context.)