Journeys are not getting assigned to employees when mass assigned from Journey Explore tab

Summary:

Hi,

We are trying mass assign a journey to all the New Hires from Journey explore tab by selecting each new hire's name with the Selection Type - "Person".

But the Journey only gets assigned to few or none of them, and the Journey Activity log only displays the employee details to whom the journey was assigned successfully.

Employees Selected in Explore Tab:

Journey Activity Tab:

Content (required):

It would be great if some one can help me in identifying what could be the reason behind the mass allocation of journeys not getting assigned to new hire's from the explore tab with the Selection type "Person".