Invalidate doesn't trigger root +layout.server load when on the root page

[CaptainCodeman]

Describe the bug

Calling await invalidate() triggers a fetch of /__data.json on any page except the root.

Reproduction

.

Logs

No response

System Info

System:
    OS: macOS 12.5.1
    CPU: (6) x64 Intel(R) Core(TM) i5-8500B CPU @ 3.00GHz
    Memory: 1.89 GB / 32.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 16.14.0 - /usr/local/bin/node
    npm: 8.3.1 - /usr/local/bin/npm
  Browsers:
    Brave Browser: 102.1.39.111
    Chrome: 104.0.5112.101
    Chrome Canary: 107.0.5260.0
    Firefox: 103.0.2
    Safari: 15.6.1
    Safari Technology Preview: 16.0
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.66 
    @sveltejs/adapter-node: next => 1.0.0-next.87 
    @sveltejs/kit: next => 1.0.0-next.437 
    svelte: ^3.49.0 => 3.49.0 
    vite: ^3.0.9 => 3.0.9

Severity

blocking an upgrade

Additional Information

I don't know if it is specific to the root route, or might be "on the same route as the layout"
I don't know if it also affects +page.server.ts load functions

I'm not using any layout groups, just plain /+layout.server.ts at the root.

Example of the issue: changing the drop-down posts to the server and calls invalidate(). The data only re-loads when not on the homepage.

Screen.Recording.2022-08-25.at.9.22.31.AM.mov

NOTE: The /__data.json that is requested when the route changes, does not contain any data.

[CaptainCodeman]

Maybe duplicate with different symptoms noticed: #6258