React Native 0.82 – JS Timers & Fetch Freeze After Launching a Non-React AppCompatActivity (Worked Fine in Earlier RN Versions)

Description

Environment

React: 19.1.1

React Native: 0.82.0

Hermes: Enabled

Platform: Android

Architecture: Reproducible on both Old Architecture & New Architecture

🚨 Summary

After upgrading to React Native 0.82.x, the JS Timers Module and Networking Module freeze whenever a non-React AppCompatActivity is launched from the app (e.g., from a 3rd-party native SDK).

This is a regression —
✅ Everything worked perfectly in RN 0.71 – 0.80
❌ The issue appears only after upgrading to RN 0.81 / 0.82

🔍 What Still Works

JS thread is alive

JS Promise microtasks execute

Native → JS events via DeviceEventEmitter work

React UI continues working

Synchronous JS code runs normally

❌ What Stops Working (Regression)

As soon as a non-React AppCompatActivity takes the foreground:

fetch() stops resolving or rejecting

setTimeout() does not execute

requestAnimationFrame() does not execute

NetworkingModule callbacks do not reach JS

TimersModule does not fire

Fetch requests still GO OUT successfully (verified via proxy tools)

Server responds, but JS never receives the response

This only happens after launching the external AppCompatActivity.

✔️ Working Behavior in Older React Native Versions

In React Native 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79 the exact same code and SDK integration works fully.

Fetch resolves normally.

Timers fire normally.

External AppCompatActivity does not impact the JS environment.

Therefore — this is a regression introduced in RN 0.81 or RN 0.82.

Steps to reproduce

Build any React Native app using RN 0.82

Integrate a simple native SDK that launches a plain AppCompatActivity (not ReactActivity)

Emit an event from the SDK → JS

Inside JS event listener:

Promise.resolve().then() → runs

setTimeout(...) → does NOT run

requestAnimationFrame(...) → does NOT run

fetch() → never resolves

Verify using proxy (e.g., Burp Suite):

Fetch does hit the server

Server sends a valid response

JS never receives the response callback

React Native Version

0.82.0

Affected Platforms

Runtime - Android

Output of npx @react-native-community/cli info

npx @react-native-community/cli -v
20.0.1
shubham.garg@GLH0CY1VHGK2 ~ % npx @react-native-community/cli info
error: unknown command 'info'
(Did you mean init?)

Stacktrace or Logs

Actual Behavior (RN 0.82 Regression)

JS thread alive

Events delivered

Timers & fetch stop working

Network request reaches server

Response returns

JS never gets the response

📌 Expected Behavior (Worked in RN ≤ 0.80)

Launching a non-React Android Activity should NOT pause RN’s TimersModule or NetworkingModule

fetch should continue resolving normally

setTimeout, RAF, requestAnimationFrame should continue executing

This is how React Native behaved for many years until RN 0.81+.

🧠 Diagnosis

Evidence indicates:

ReactContext timers + networking modules get suspended when a non-React AppCompatActivity becomes active.

JS microtasks still run → JS engine (Hermes) alive.

NetworkingModule native → JS callback never fires → indicates bridge suspension.

This DID NOT occur in earlier RN versions.

You can check our sample app https://github.com/payu-intrepos/payu-non-seamless-react

MANDATORY Reproducer

https://github.com/ShubhGar/RN-Fetch-issue

Screenshots and Videos

No response

Inizia eseguendo il riproduttore obbligatorio all’indirizzo github.com/ShubhGar/RN-Fetch-issue con React Native 0.82.0, quindi confronta il comportamento con le versioni precedenti elencate. Concentrati sulla transizione quando una AppCompatActivity non-React passa in primo piano e verifica che le callback di fetch, setTimeout e requestAnimationFrame riprendano o continuino a essere eseguite come previsto.