Loading screen on every route change after migrating to Next.js 15

[matpiwowarski]

Summary

After upgrading from Next.js 14 to 15 and React 18 to 19, a visible loading screen appears on every route change, even when navigating between statically generated pages.

No relevant code changes were made during the upgrade.

Any ideas what could be the reason?

Additional information

I'm using App Router.

Example

No response

[icyJoseph]

Any chance you could tweak, https://stackblitz.com/edit/nextjs-wvk44qu1 to a minimal reproduction of the issue you see? Share back the forked link.