Could you please try saving your site permalink settings?
If it still happens then would you mind if i log in to your site and do some troubleshooting? If this is ok then could you please share me your site log in details privately by adding them in the box having text “Click here to share private content. Only you and forum moderators will be able see it.”?
don’t know what happened or what I did, but today the website is working fine: when I click on a portfolio category, the category page opens right without showing the author and that’s perfect!