Many people reuse their personal passwords for everything. As a security measure, after the first time a volunteers is sent their assigned password in the Web Terminal, the password then is shown as "[secret]" within MSP or as "[removed for security]" in emails. This is intentional to guard the privacy of the volunteers.
For help with how volunteers can recover passwords, please see this post on our blog.
As the administrator you can reset volunteers passwords by following the steps in this article.