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Description
Please provide all the information requested. Issues that do not follow this format are likely to stall.
Description
Before upgrading, my app was on RN 0.61.5. No issue on cpu pegged at 100%.
After upgrade to 0.62.1, on certain number crunching in JS and I can't identify exactly in what yet (reason below). I'm getting 100% cpu pegged and app completely stalled from doing anything else, though UI is not frozen. This is due to JSC is completely blocked. This is when app is built in release mode, and so JSC is run on real device (iPhone X)

If I rebuilt app in Debug mode, running on same real device, and doing same UX on app. No more issue as JS processing is run in Chrome's V8 instead:

React Native version:
System:
OS: macOS 10.15.4
CPU: (16) x64 Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz
Memory: 2.00 GB / 40.00 GB
Shell: 5.7.1 - /bin/zsh
Binaries:
Node: 13.12.0 - /usr/local/bin/node
Yarn: 1.22.4 - /usr/local/bin/yarn
npm: 6.14.4 - /usr/local/bin/npm
Watchman: 4.9.0 - /usr/local/bin/watchman
Managers:
CocoaPods: 1.9.1 - /usr/local/bin/pod
SDKs:
iOS SDK:
Platforms: iOS 13.4, DriverKit 19.0, macOS 10.15, tvOS 13.4, watchOS 6.2
Android SDK:
Android NDK: 21.0.6113669
IDEs:
Android Studio: 3.5 AI-191.8026.42.35.6010548
Xcode: 11.4/11E146 - /usr/bin/xcodebuild
Languages:
Python: 2.7.16 - /usr/bin/python
npmPackages:
@react-native-community/cli: Not Found
react: 16.11.0 => 16.11.0
react-native: 0.62.1 => 0.62.1
npmGlobalPackages:
*react-native*: Not Found
Steps To Reproduce
Provide a detailed list of steps that reproduce the issue.
I can't list repro steps as I'm not sure what in my JS code is triggering the 100% cpu in JSC, that doesn't occur in Debug mode V8. But there's clearly something changed from RN 0.61 -> 0.62 upgrade that changed it.
And since I can't debug while the JSC cpu pegged occurs only in Release mode, this makes this a Heisenbug. How do I debug when app in debug mode doesn't manifest the same issue that's in release?
Expected Results
JSC not stalled in Release mode on device