Svelte 5: Cannot read properties of null (reading 'isConnected')

[otodockal]

Describe the bug

On route navigation in SvelteKit (together with Svelte 5 runes), I encountered the error Cannot read null properties (reads 'isConnected'). There might be a bug related to snippet_effect or create_snippet_block fns...At some point block.d becomes [null] for some reason.

Reproduction

• svelte 5.0.0-next.15
• @sveltejs/kit 1.27.6

https://github.com/otodockal/svelte-5-runes-bug
In order to reproduce the bug check this line:
https://github.com/otodockal/svelte-5-runes-bug/blob/main/src/routes/%2Bpage.svelte#L8

Logs

reconciler.js:66 Uncaught TypeError: Cannot read properties of null (reading 'isConnected')
    at remove (reconciler.js:66:13)
    at render.js:3186:5
    at destroy_signal (runtime.js:1052:3)
    at destroy_references (runtime.js:387:5)
    at destroy_signal (runtime.js:1031:2)
    at render.js:1473:3
    at destroy_signal (runtime.js:1048:4)
    at destroy_references (runtime.js:387:5)
    at execute_effect (runtime.js:423:3)
    at render (render.js:1703:5)
remove @ reconciler.js:66
(anonymous) @ render.js:3186
destroy_signal @ runtime.js:1052
destroy_references @ runtime.js:387
destroy_signal @ runtime.js:1031
(anonymous) @ render.js:1473
destroy_signal @ runtime.js:1048
destroy_references @ runtime.js:387
execute_effect @ runtime.js:423
render @ render.js:1703
(anonymous) @ render.js:1717
execute_signal_fn @ runtime.js:287
execute_effect @ runtime.js:427
flush_queued_effects @ runtime.js:475
process_microtask @ runtime.js:494

System Info

  System:
    OS: macOS 12.0.1
    CPU: (8) arm64 Apple M1
    Memory: 84.72 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 20.0.0 - ~/.nvm/versions/node/v20.0.0/bin/node
    Yarn: 1.22.18 - /opt/homebrew/bin/yarn
    npm: 9.6.4 - ~/.nvm/versions/node/v20.0.0/bin/npm
    pnpm: 8.11.0 - ~/Library/pnpm/pnpm
    bun: 0.7.1 - ~/.bun/bin/bun
  Browsers:
    Chrome: 119.0.6045.159
    Safari: 15.1
  npmPackages:
    svelte: 5.0.0-next.15 => 5.0.0-next.15 

Severity

annoyance

[dummdidumm]

Could you provide a reproduction with the offending code?

[otodockal]

I'll try to get a simplified version here ASAP. Once it's ready I'll let you know. I should have created it first...

[otodockal]

@dummdidumm I added repro in the description now and in this comment:
#9675 (comment)