Patient/Subject Hand Of Mode locks the app on the current form to prevent navigation out of it. The user sign-in is then required to unlock it.

Handoff mode is a tool which allows a clinician to handoff their mobile device to a patient for a form to be completed on site, or in a more controlled setting. This prevents the need for the patient to directly log in with their own sign in credentials.  You can perform handoff in single form mode or bundled form mode.

The user role which needs access to handoff mode must have the permission in role security under the Subject Record Management application. Typically this would be the patient-facing clinician at a site, such as a Research, Study or Data Coordinator.

Second, the form which needs to be handoff mode-capable must be an ePRO form, as set in the form properties of the form builder.

Read further on how to verify "Single Handoff Mode" is enabled and how it works and how "Bundled Handoff Mode" works here.