A user with user level privilege on a record and have global level depth to assign, when reassign that record to a user in a different Business Unit gets an error that he doesn't have read privilege on that records.

When checked the record from an admin user, the record is reassigned sucessfully and since the user who have assigned the record doesn't have the read privilege anymore due to which we're getting the error.

Ask : It would have been great if it goes back to the view instead of showing the error to avoid confusion.