Upgrade 1.1 to 1.2 - route problems

I had a Neos website running 1.1 and I’ve upgraded via composer to 1.2 using the guide here:

Unfortunately after the upgrade, none of the website links work. In FE when I try to access a page, I get: Page not found
In BE, when I access a page, no error is shown, but it redirects to the root page.

Looking in the Neos logs, I see when I access a page:
Router route(): No route matched the route path “page-name”

Any hints what I need to do, there is a lot of content. Also, new created pages have the same problem.