Child route HydrateFallback is never rendered

[jbojcic1]

Reproduction

Open https://stackblitz.com/edit/github-dw4udjbs and start the app in standalone window. Open the console then go directly via url to /parent/child route.

System Info

System:
    OS: macOS 15.6
    CPU: (10) arm64 Apple M1 Max
    Memory: 5.63 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.18.0 - ~/.local/state/fnm_multishells/3135_1755672991394/bin/node
    Yarn: 1.22.22 - /opt/homebrew/bin/yarn
    npm: 10.9.3 - ~/.local/state/fnm_multishells/3135_1755672991394/bin/npm
    pnpm: 10.13.1 - /opt/homebrew/bin/pnpm
    bun: 1.2.19 - /nix/store/l08n46gh7klp2k7nyvmnx79f8p4hysfn-bun-1.2.19/bin/bun
  Browsers:
    Brave Browser: 136.1.78.97
    Chrome: 139.0.7258.138
    Safari: 18.6
    Safari Technology Preview: 26.0
  npmPackages:
    @react-router/dev: 7.8.1 => 7.8.1 
    @react-router/express: 7.8.1 => 7.8.1 
    @react-router/fs-routes: 7.8.1 => 7.8.1 
    @react-router/node: 7.8.1 => 7.8.1 
    react-router: 7.8.1 => 7.8.1 
    vite: 6.3.5 => 6.3.5

Used Package Manager

npm

Expected Behavior

I expected to see Parent route is loading... while parent's clientLoader is running and then Child route is loading... while child's clientLoader is running.

Actual Behavior

I only see Parent route is loading... and Child route is loading... is never shown.

[brophdawg11]

That's not how HydrateFallback is designed. It's intended to be a singular UI to display while everything loads - specifically to avoid "popcorn UI" as things load in and prevent the UI from changing/shifting in front of the users eyes.