Weird!Windows Credentials auto delete after a certain time

[antares]

Hi all, I created a Windows Credential (Control Panel/Credential Manager/Windows Credential/Add a Windows Credential) for my external Synology NAS so that I don't have to input my NAS username and password each time I want to map the NAS as a drive in Windows Explorer. The strange thing is that the credential is created successfully but after a certain time, or after reboot it disappears from the list as if auto deleting itself. Any idea whats happening? Thanks