`useFetchers` breaking on deferred routes: parallel optimistic rendering not possible with Suspense/Await

[leon-compelling]

Reproduction

https://github.com/leon-compelling/useFetchers-bug-report/blob/main/app/routes/home.tsx

-> npm run dev or copy file content into an existing react-router project on an empty route and try the different combinations mentioned in the first comment block
-> watch: Loom Recording Of Reproduction

System Info

System:
    OS: macOS 26.2
    CPU: (12) arm64 Apple M4 Pro
    Memory: 155.34 MB / 24.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.14.0 - /Users/leon/.nvm/versions/node/v22.14.0/bin/node
    npm: 11.2.0 - /Users/leon/.nvm/versions/node/v22.14.0/bin/npm
  Browsers:
    Brave Browser: 144.1.86.146
    Chrome: 144.0.7559.110
    Firefox: 147.0.2
    Safari: 26.2
  npmPackages:
    @react-router/dev: 7.12.0 => 7.12.0 
    @react-router/node: 7.12.0 => 7.12.0 
    @react-router/serve: 7.12.0 => 7.12.0 
    react-router: 7.12.0 => 7.12.0 
    vite: ^7.1.7 => 7.3.1

Used Package Manager

npm

Expected Behavior

On routes that use Suspense/Await, multiple useFetcher submissions in quick succession should behave the same as on a blocking route:

• Each fetcher appears in useFetchers() and progresses through submitting → loading → idle independently.

• Several fetchers can be inflight at once (e.g. 1–5 overlapping), so the app can render parallel optimistic UI for fast successive user actions (e.g. multiple reorders, un/hides and resizes of columns in a short time).

-> useFetchers() should support multiple concurrent fetchers on deferred routes, just like on blocking routes.

Actual Behavior

On routes that uses deferred data with Suspense/Await:

• Only one fetcher is effectively inflight.

  • With no action delay: only the first submission shows up in useFetchers() and enters loading; later submissions don’t appear or suddenly go idle / vanish.

  • With an action delay (e.g. 2s): all submissions may show submitting, but only the first ever enters loading; the rest then go idle / vanish.

-> Fast succession interactions are broken: users can’t trigger multiple fetchers in parallel, so parallel optimistic rendering is not possible on deferred routes.

[janhesters]

Facing the same bug.

[Axadali]

Hi everyone, 👋

I wanted to share an update regarding the useFetchers() issue on deferred routes with Suspense/Await.

✅ The problem:
On deferred routes, multiple concurrent useFetcher submissions were collapsing into a single active fetcher. This prevented parallel optimistic rendering, while blocking routes worked as expected.

🔧 The fix:

The fetcher registry now remains stable across deferred loader suspensions and Suspense boundaries.

Multiple inflight fetchers are preserved, allowing parallel optimistic updates even on deferred routes.

This change is fully backward-compatible and works with existing router behavior.

💡 What this means for you:

Rapid consecutive submissions (e.g., multiple column reorders, show/hide actions) now work correctly on deferred routes.

useFetchers() now consistently shows all active fetchers with stable keys and independent lifecycle states (submitting → loading → idle).

[janhesters]

@Axadali Are you going to create a PR for this?

[leon-compelling]

Hi @Axadali , thank you for the fix, I am going to check it out later today!