Hey there, let's work through this frustrating issue you're hitting—after closing and reloading your React Native iOS app, the progress screen freezes then goes blank, plus you get that scary "RCTBridge required dispatch_sync to load RCTDevLoadingView This may lead to deadlocks" warning. I’ve helped debug this a few times, so here are the most reliable fixes to try:

1. Clean All Caches & Rebuild from Scratch #

More often than not, stale cache is the culprit here. Let’s wipe everything and start fresh:

• Clear npm/yarn cache: npm cache clean --force (or yarn cache clean if you use yarn)
• Delete and reinstall dependencies: rm -rf node_modules && npm install
• Clean Xcode’s build folder: Open Xcode, go to Product > Clean Build Folder (or hit Cmd + Shift + K)
• Delete Xcode’s DerivedData: Navigate to ~/Library/Developer/Xcode/DerivedData and delete the folder matching your project name
• Restart Metro with cache reset: Kill your current Metro server, then run npx react-native start --reset-cache

2. Fix Threading Issues in RCTDevLoadingView Calls #

The warning specifically calls out dispatch_sync on the RCTBridge, which means something’s trying to load the dev loading view synchronously on the main thread—this can block the bridge initialization and cause the blank screen.

• If you’ve customized your app’s loading logic (like in AppDelegate.m or a custom native module), check for any dispatch_sync calls related to RCTDevLoadingView or RCTBridge modules. Replace them with dispatch_async to avoid blocking the main thread.
• Example fix in Objective-C:

  // Instead of this (synchronous, risky)
  dispatch_sync(dispatch_get_main_queue(), ^{
    [bridge moduleForClass:[RCTDevLoadingView class]];
  });
  
  // Use this (asynchronous, safe)
  dispatch_async(dispatch_get_main_queue(), ^{
    [bridge moduleForClass:[RCTDevLoadingView class]];
  });
  

3. Check Third-Party Library Compatibility #

Outdated or poorly maintained native modules sometimes use deprecated synchronous bridge calls that trigger this warning.

• Identify any recently added libraries (especially native iOS modules) and try removing them temporarily to see if the issue goes away.
• Update your React Native version to the latest stable patch release (make sure it’s compatible with your dependencies) — newer versions fix many threading-related bugs in the bridge.

4. Verify AppDelegate Configuration #

If you’ve modified your AppDelegate.m/AppDelegate.swift to customize bridge initialization, double-check that you’re not blocking the main thread during setup.

• Avoid calling moduleForClass or any bridge-related methods synchronously right after initializing the RCTBridge. Let the bridge finish initializing asynchronously before accessing modules.
• Stick to the default bridge initialization code as much as possible unless you have a specific need to customize it:

  RCTBridge *bridge = [[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];
  RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:bridge
                                                   moduleName:@"YourAppName"
                                            initialProperties:nil];
  

5. Temporary Workaround: Disable RCTDevLoadingView #

If none of the above work immediately, you can temporarily disable the dev loading view to unblock development (note: this is a band-aid, not a permanent fix):

• Create an empty file empty.js in your project root with just export default {};
• Update your metro.config.js to redirect RCTDevLoadingView requests to this empty file:

  module.exports = {
    resolver: {
      resolveRequest: (context, moduleName, platform) => {
        if (moduleName === 'RCTDevLoadingView' && platform === 'ios') {
          return {
            filePath: require.resolve('./empty.js'),
            type: 'sourceFile',
          };
        }
        return context.resolveRequest(context, moduleName, platform);
      },
    },
  };
  

Start with the cache cleaning step—it’s quick and fixes most cases. If that doesn’t work, move on to checking threading in your native code and third-party libraries.

内容的提问来源于stack exchange，提问作者ronak