[Worklets] Tried to modify key 'value' … warnings + thrown non-worklet function 'addListener' on the UI thread with react-native-worklets 0.8 (Reanimated 4 / RN 0.85 / New Architecture)

[augustosamame]

Description

When any component using KeyboardProvider / KeyboardAwareScrollView mounts, the dev console is flooded with
Reanimated/Worklets warnings, and a worklet throws in development:

[Worklets] Tried to synchronously call a non-worklet function `addListener` on the UI thread.

This happens on both iOS and Android, on app startup (the providers wrap the root), and repeats on every screen
that mounts a keyboard-aware view. The app remains functional (the thrown error is shown as a dev redbox/LogBox), but
it makes development very noisy and is non-suppressible from app code, since the throw originates inside
react-native-worklets.

Environment

Package	Version
react-native-keyboard-controller	1.21.8
react-native	0.85.3
react-native-reanimated	4.3.1
react-native-worklets	0.8.3
react-native-screens	4.25.1
react-native-safe-area-context	5.7.0
react	19.2.3
expo	56.0.3 (SDK 56)
Architecture	New Architecture (Fabric/bridgeless), Hermes
Platforms	iOS (Simulator + device) and Android (emulator)
Babel	babel-preset-expo (injects react-native-worklets/plugin automatically; confirmed not double-applied)

Steps to reproduce

1. Expo SDK 56 / RN 0.85 app with the New Architecture, Reanimated 4.3.1 + Worklets 0.8.3.
2. Wrap the app root in <KeyboardProvider> and render any screen using KeyboardAwareScrollView (e.g. a simple
   login form).
3. Run a dev build (expo run:ios / expo run:android) and open the screen.

Minimal component:

import { KeyboardProvider, KeyboardAwareScrollView } from 'react-native-keyboard-controller';

export default function App() {
  return (
    <KeyboardProvider>
      <KeyboardAwareScrollView>
        <TextInput placeholder="email" />
        <TextInput placeholder="password" secureTextEntry />
      </KeyboardAwareScrollView>
    </KeyboardProvider>
  );
}

Expected behavior

Keyboard-aware scrolling works with no Worklets warnings or thrown errors.

Actual behavior

A burst of warnings (8+ per mount):

WARN  [Worklets] Tried to modify key `value` of an object which has been already passed to a worklet.
https://docs.swmansion.com/react-native-reanimated/docs/guides/troubleshooting#tried-to-modify-key-of-an-object-which
-has-been-converted-to-a-serializable

followed by a thrown error:

ERROR  [Error: [Worklets] Tried to synchronously call a non-worklet function `addListener` on the UI thread.
https://docs.swmansion.com/react-native-worklets/docs/guides/troubleshooting#tried-to-synchronously-call-a-non-workle
t-function-on-the-ui-thread]

A representative call-stack frame points at valueUnpacker (worklet value deserialization on the UI runtime).

Investigation / likely cause

Both messages originate in react-native-worklets 0.8:

• "Tried to modify key 'value' …" → logger.warn in
  react-native-worklets/lib/module/memory/serializable.native.js (~line 542).
• "… non-worklet function 'addListener' on the UI thread" → thrown in
  react-native-worklets/lib/module/threads.native.js (~line 188; in dev a remote/JS function called on the UI runtime
  throws to point users at runOnJS).

It appears the keyboard handler captures the FocusedInputEvents event-emitter object (which exposes addListener)
into a worklet/shared value, and worklets 0.8's stricter serialization then (a) warns when that captured object is
mutated, and (b) throws when addListener is invoked during unpacking on the UI thread. The relevant site in this
package — react-native-keyboard-controller/lib/module/animated.js:

import Reanimated, { useSharedValue } from "react-native-reanimated";
import { FocusedInputEvents, /* ... */ } from "./bindings";
// ...
const progressSV = useSharedValue(0);
const heightSV   = useSharedValue(0);
const layout     = useSharedValue(null);
// ...
const subscription = FocusedInputEvents.addListener("layoutDidSynchronize", () => { /* ... */ });

(plus several "worklet" handlers in the same file). This pattern worked under older worklets versions but trips
worklets 0.8's serialization rules under the New Architecture.

Workaround

configureReanimatedLogger({ strict: false }) quiets the warnings but not the thrown error. We replaced
KeyboardAwareScrollView/KeyboardProvider with a small wrapper over React Native's KeyboardAvoidingView +
ScrollView, which avoids worklets entirely.

Additional notes

• Reproduces with the exact versions Expo SDK 56 pins (expo install reports them as up to date), so it isn't a
  user version mismatch.
• Dev-only (__DEV__) — release builds don't surface the messages, but the underlying worklet behavior is still a
  smell.
• Ruled out: verified a single instance of react, react-native, react-native-reanimated, and react-native-worklets
  (single hoisted copy, no nested duplicates, no self-reference symlinks, default Metro resolver, Yarn 1 workspace).
  So this is not the duplicate-instance / self-referencing-package class of issue that's commonly blamed for these
  worklet errors.
• Happy to provide a minimal reproducible repo if helpful.

[pitahorn]

When migrating to Expo 55, we hit this exact error on our UI thread:

  ERROR  [Worklets] Tried to synchronously call a non-worklet function
  `addListener`
  WARN   [Worklets] Tried to modify key `value` of an object which has been already
  passed to a worklet.

It fired repeatedly on app mount, with:

• expo 55
• react-native 0.83
• react 19.2
• New Architecture / Hermes
• react-native-reanimated 4.2.1
• react-native-worklets 0.7.4 (SDK 55's bundled versions)
• react-native-keyboard-controller 1.20.7

While ruling out other options, we suspected keyboard-controller's FocusedInputEvents.addListener("layoutDidSynchronize") in animated.js, but it turned out NOT to be keyboard-controller.

Sharing the elimination in case it saves others time. None of these were the cause:

1. A double worklets babel plugin registration (the preset auto-injects
   react-native-worklets/plugin and we also had a manual entry) — removed it, throw
   persisted.
2. The react-native-dotenv / env-inlining plugin breaking EXPO_OS issue from
   Crash with Expo SDK 55: [Worklets] Tried to synchronously call a non-worklet function 'addListener' on the UI thread #1325 — we had no such plugin and no EXPO_OS is not defined warnings.
3. Our own app code — no addListener inside any of our worklets.
4. A dual-version worklets install — verified single copy, plugin and runtime
   both 0.7.4.
5. React Compiler — not enabled.

We also tried bumping to react-native-reanimated 4.3.1 + react-native-worklets 0.8.3 (the serialization rewrite) but the throw still fired.

Removing keyboard-controller completely by uninstalling the dependency, removing all usage (KeyboardProvider + KeyboardAwareScrollView/KeyboardStickyView), and regenerating the native project from scratch confirmed zero KeyboardController:: native events in logcat, but the error and warn logs still fired.

This rules out that keyboard-controller is not required to reproduce this. We found several issues on other react native libraries built on reanimated that had similar issues, but those fixes did not work for us either. (See react-native-reanimated-carousel#900)

We think that the promblem is reanimated's own SharedValue / mapper serialization , with keyboard-controller being just one of several consumers that trigger it.

My guess is this hasn't reproduced in this repo's example apps because they pin react-native 0.81.4, while every report we've seen of this throw is on RN 0.83+. The triggering combination appears to be RN 0.83+ × worklets 0.7.4+ × New Architecture — bumping the example apps to RN 0.83 may surface it.