SvelteKit container on Azure App Service page rewrite issue /project/1 being ameneded to /project/undefined/project/1?

I have a SvelteKit with Svelte 5 application which I am deploying to the Azure App Service inside of a Docker container.

I have routes with a parameter set up like:

route/  - project       - [id]+page.svelte+page.ts

When I test running the container on my local, http://localhost:3000/project/1 everything works fine and as expected.

When I deploy the container to the Azure App Service, none of my parameterised routes resolve successfully.

When I go {APP_URL}/project/1 then in the http logs I can see:

2025-04-04T10:44:48.143377680Z SvelteKitError: Not found: /project/undefined/project/12025-04-04T10:44:48.144560408Z     at resolve2 (file:///app/build/server/index.js:5444:18)2025-04-04T10:44:48.144571388Z     at resolve (file:///app/build/server/index.js:5269:34)2025-04-04T10:44:48.144574191Z     at Object.handle (file:///app/build/server/chunks/hooks.server-4c2e5641.js:2:26)2025-04-04T10:44:48.144576962Z     at respond (file:///app/build/server/index.js:5267:43)2025-04-04T10:44:48.144579396Z     at async Array.ssr (file:///app/build/handler.js:18942:3) {2025-04-04T10:44:48.144589185Z   status: 404,2025-04-04T10:44:48.144591757Z   text: 'Not Found'2025-04-04T10:44:48.144594560Z }

I am not setting any redirects myself. What can be causing the appearance of the /project/undefined in the request which my containerized application is receiving?