I was seeing this same behavior on my test setup, over and over again. I clear the cache, it works again, then again, it shows up. In a desperation moment, I check:
Same behavior. When entering your shop, it shows the catalogs on the left. I click the “Demo Catalog” link:
It works. After a while, adding to cart, clicking the breadcrumbs, if I go back to the above link, it redirects to:
I get: “Category not found for Category ID !”
If I clear my cache, normal operation. I’m at a loss at why this happens. Using firefox.