Sudden major permalink issues

To preface this, all of this functionality was working recently.

It’s related to portfolios.

Suddenly (perhaps after some recent plugin update or change in wind direction:) ) I started getting 404s on all my portfolio ‘items’.

Portfolio list works ok.

I switched permalinks to default (numeric). And suddenly portfolio items like the below started showing:
http://www.dasilvamotorsport.com/portfolio-item/honda-nsx/

But portfolio category doesn’t show:
http://www.dasilvamotorsport.com/performance-project-portfolio/

Switching back to postname as permalink basically reverts back to the original issue that portfolio items don’t show up. I had heard that permalinks may need a refresh but this hasn’t helped me.

Again, all of this was working perfectly a couple of weeks ago so really not sure what happened. Is there something I can debug or try?

Appreciate any help on this.

Nik