When testing and troubleshooting access and data security, it is often necessary to act as another user.
It should be possible for an admin user to sign in but act as another user.
A control could be in place for a user to be required to authorize admin access as them as is done in Salesforce.
Alternatively, user in question could be added to an "Impersonation" group
Essentially an admin would authenticate and then select "Act-as user" and select a user and loose their admin capabilities.
Several other tools have this and it is a gap.