i have same problem when upgrade to v19. I realized that the problem was because I was making my API calls like this. http.get("api/apiadress") I'm using a middleware (http-proxy-middleware) in the server.ts file and prerender was working without any problems in v18.

When I updated to v19 I now noticed that API calls start with address "ng-localhost". The problem was solved when starts with http://localhost or http://127.0.0.1 to API calls.