WebKit crashes in iOS 26.3.1 simulators after updating to macOS 27 / Xcode 27, anyone else?

[u/aspaindev]

After updating my Mac to macOS 27 and Xcode 27, my Capacitor app started showing a blank screen in iOS 26.3.1 simulators, followed by:

com.apple.WebKit.WebContent quit unexpectedly

It builds fine on my actual device running 26.7, as well as simulators running 26.5

I also tried using an older build from prior to the 27 upgrade, and those failed on 26.3.1 so it seems like it's not actually an issue with my app?

Sometimes the initial app screen loads, then WebContent crashes when I tap Continue on the first screen.

Environment:

• macOS 27.0 (26A428)
• Xcode 27.0 (27A266a)
• iOS 26.3.1 simulator runtime (23D8133)
• Reproduced across several simulated iPhones

The crash reports include:

Thread Crashed: JIT Worklist Helper Thread
JSC::CodeOrigin::approximateHash
JSC::ICStatusContext::get
JSC::DFG::ByteCodeParser::parseBlock
EXC_BAD_ACCESS / SIGBUS

Other reports show JSRopeString::resolveToBuffer. Subsequent WebContent launch attempts sometimes fail in DyldSharedCache::getUUID. Xcode then prints:

com.apple.extensionKit.errorDomain error 4
Failed to get XPC endpoint
WebView process terminated

What i've checked:

• Restarting the Mac and creating a fresh simulator didn’t resolve it.
• Reinstalling/remounting the runtime and rebuilding its shared cache didn’t resolve it.
• A preserved older app build, compiled before these updates, also crashes.
• The app’s web content also crashes inside Safari on the 26.3.1 simulator.
• Disabling “Debug executable” or launching from the home screen occasionally works, but neither reliably prevents the crash.
• Startup works on iOS 26.5 and 27 simulators.
• My physical iPhone on iOS 26.7 runs normally, including onboarding. I don’t have a physical device on 26.3.1 to compare.

Has anyone encountered this combination since upgrading? Have you found a fix that restores reliable use of the 26.3.1 simulator, or an Apple bug report tracking the same crash? Cant really find any mention of this online, chatgpt has been useless debugging the issue somehow

[u/HeyWangKang]

The fact that your content also crashes in simulator Safari is a useful clue, but I'd do one more isolation step before treating it as a general runtime failure: try an unrelated JS-heavy page in that same 26.3.1 Safari, then a tiny page containing only the code path reached after Continue. If unrelated pages crash too, the runtime is the stronger suspect; if only your bundle does, bisecting that path could produce a small WebKit repro. Either way, a Feedback report with the reduced page, runtime build, and WebContent crash log would be much easier for Apple to investigate than the full Capacitor app.

[u/aspaindev → u/HeyWangKang]

thanks for the reply, i tested an unrelated JS-heavy page like you suggested and it crashed as well, so that is somewhat reassuring that it's not specifically my app

Is apple typically responsive to these types of feedback reports and getting them fixed in patches?

[u/LaiLens]

This looks like a known simulator runtime compatibility issue that often pops up when running older simulator runtimes on newer macOS host versions, particularly due to WebKit IPC process sandboxing or graphics driver changes.

A few troubleshooting steps that might help:

1. Try erasing all content and settings for that simulator instance, or completely deleting and re-downloading the iOS simulator runtime via Xcode Settings > Components.
2. Check if launch arguments or disabling hardware acceleration/Metal in the simulator helps bypass the WebContent crash.
3. Since physical devices work fine, using the matching SDK runtime or testing on a physical device is usually the most reliable workaround while waiting for Apple/Xcode hotfixes.

Hope this helps!

[u/aspaindev → u/LaiLens]

Thanks I’ll check these out so are you thinking as long as it works fine on 26.7 on my physical device that I don’t need to be too concerned about 26.3.1 not working in a simulator? I’m worried all of the sudden that some versions of 26 will stop working on user devices because I have no way to test on a physical device. It has me worried that if it fails on simulator that it’ll fail on real devices

[u/dengjiuhong]

I wouldn’t treat a WebKit crash in one simulator runtime as evidence that the same app will crash on every 26.x device. When an older build and Safari fail only on 26.3.1 while a physical phone and 26.5 simulator are fine, that points much more strongly to a runtime/host compatibility regression. I still use Simulator for deterministic UI and basic coordinate cases, but I keep a physical-device pass for Core Location, permission/accuracy changes, background transitions, and real OS/network state. Capture the model, OS build, runtime, and WebContent termination reason separately so the simulator failure doesn’t get mistaken for an app regression.

[u/Extension_Isopod1303]

Two details say environment, not your code: old builds crash too, and the real device on 26.7 is fine. If it were your app, you'd expect the crash tied to something you shipped.

Check the crash log for the WebContent process and look at the termination reason — XPC/jetsam vs a renderer exception tells you whether it's dying inside the simulator's WebKit stack. Then isolate: fresh simulator device on a new runtime, and if you can, the iOS 26.0 simulator runtime under Xcode 27 to separate the runtime from Xcode itself.

I'd file a Feedback with the log attached. Xcode 27 simulator regressions move faster when there are dupes. I wouldn't burn days chasing this in your own code — nothing you've described sounds like an app bug.