When using digital Signature, user has to "login" to digital ID file to use it

we use a log of digital signatures. each users adobe is configured to allow them to draw the rectangle signature option.

lately, one user, when she goes to sign a pdf, it asks her to create a new signature, although she would have one already.

when i got to "Edit, Preferences, Signatures, Identities & Trusted Certificates" , then Digital ID file, its status is set to "logout"

once we log back in, she can then use the rectangle signature option.

Can you advise, why adobe is logging out the Digital ID file?

thanks

Using AdobePro XI