This could be due to the API version used to import the Salesforce object to PowerCenter.
Some columns are visible in higher API versions and if lower API version is used to import those objects, new columns (visible in higher API version) would not be visible.
Check the API version you are using within PWX Salesforce and the API version when the columns were added in Salesforce.
It would be helpful, if you can share the version of your PowerCenter server. Also API version that you are using to import in PowerCenter. You will see the same behavior if you login to Salesforce using the same API version used in the PowerCenter.