最终，答案是我没有从用户ID中删除Facebook_。因此，我理论上是将我的Cognito电子邮件/密码链接到'Facebook_USERID'而不是'USERID'。

进行了此更改后，我就可以通过1个关联的帐户进行身份验证。

// Get Email
        var params = {
          UserPoolId: 'YOUR_USER_POOL',AttributesToGet: ['sub','email'],Filter: "email = \"" + event.request.userAttributes.email + "\""
        }
        cognito.listUsers(params,(err,data) => {
            if (err) {
                console.log(err,err.stack);
            }
            else {
                console.log(data);
                console.log(event.userName);
                if(data != null && data.Users != null && data.Users[0] != null)
                {
                  console.log(data.Users[0].Username);
                  var params = {
                    DestinationUser: { 
                      ProviderAttributeValue: data.Users[0].Username,ProviderName: 'Cognito'
                    },SourceUser: { 
                      ProviderAttributeName: 'Cognito_Subject',ProviderAttributeValue: event.userName.split("_")[1],ProviderName: 'Facebook'
                    },UserPoolId: 'YOUR_USER_POOL'
                  };
                  cognito.adminLinkProviderForUser(params,function(err,data) {
                    if (err) console.log(err,err.stack); // an error occurred
                    else     console.log(data);           // successful response
                  });
                }
            }
        });