Candidate details not saved on career center

Summary

When applying for a new job, the information of a candidate is not appearing on the form

Content

There are two candidates (say 'x' and 'y') who have a login for the career center to apply for jobs. Both have entered their personal details before for other applications. When 'x' wants to fill in a new application, a lot of fields are already filled in based on former applications, but when 'y' wants to fill in a new application, all fields are empty and he has to fill in everything all over again.

Does anybody know what causes this?