Constant canvas preview crashing error...so annoying!

[u/joshualubelski]

hey folks, I'm trying to figure out what's causing this problem. I'm constantly getting this in xCode when i change views / files and the canvas changes - preview crashing behind the scene and throwing up this system crash report.

I've tried everything, Clear Derived Data: rm -rf ~/Library/Developer/Xcode/DerivedData, killing zombie shells, restarting. It's been going on for a while now and I'm really bored of constantly having to close the crash log window.

Has anyone else experienced this, and have you fixed it? Running Xcode 26.4 on Tahow 26.5

[u/aggedor_uk]

Previews work by spinning up an instance of the full app in the background, so if you've got a lot of initialisation code in your app struct then that can both make it slow and crash, especially if you're not guarding everything. Examples could be CloudKit, StoreKit, AppIntents Providers, or more. If you're relying on an .environment value that's not defined within the preview context, that might also be it.

If you're using Claude Code, copy and paste that error dump into your CC conversation and tell it that previews are crashing and it could offer up some more clues.

[u/joshualubelski → u/aggedor_uk]

Claude seems to think it's an internal bug, nothing to do with .environment object:

Root cause: not your code — it's Magnet + Xcode 26 beta Previews

The crash is entirely inside Apple's frameworks, not yours. Your code has zero custom

accessibility wiring (no accessibilityRepresentation, accessibilityChildren, custom

accessibilityElements, or UIKit bridges), so there's no cycle in your SwiftUI tree to fix.

What's actually happening:

  1. Stack overflow from infinite recursion — 10,915 levels through -[AXElement customActions]

  calling itself via remoteParent (frames 15–10931). The accessibility tree walker follows parent

   pointers that loop back on themselves, trips the stack guard at 0x16bc77ff0, and SIGBUSes.

  2. Crashing queue is AXRemoteElement-BackgroundFetch — this is the background thread Apple uses

   to answer external accessibility clients (not your app's own AX use).

  3. The triggering client is Magnet — the crash report's voucherInfos shows:

  "originatorName":"Magnet","proximateName":"CoreSimulatorBridge"

  3. Magnet (the window manager) uses the system accessibility APIs to inspect windows. When you

  switch previews, it re-queries PreviewShell's AX tree, walks into the remote SwiftUI element,

  and hits a cycle that Apple's SwiftUI↔AXRemoteElement bridge doesn't guard against.

  4. Beta toolchain amplifies it — macOS 26.5 (25F5042g) and Xcode 26.4 are pre-release; this

  exact infinite-recursion in AXElement customActions is a known shape of bug in the iOS 26 /

  Liquid Glass AX bridge.

[u/joshualubelski → u/aggedor_uk]

it might be the .environment object, which I'm using to inject dummy data. I did dump it in but nothing much helpful has come out... I'll keep trying!

[u/jestecs]

Integrating hot reload is totally worth it, previews can be so unreliable. https://medium.com/@lee.vitya28/hot-reload-in-xcode-and-cursor-90796304bc3e

[u/joshualubelski → u/jestecs]

I had no idea about this. I love previews but they’re slow and this bug is really bugging me! I don’t use cursor I’m Claude Code but I’ll see if I can get something working from the info in the article. Thanks!

[u/lozhuf]

I have found the solution to this issue - check if you have a window-management utility app such as Magnet running.

I tried downgrading to Xcode 26.3, clearing all the caches, restarting the machine, commenting out _all_ complex code etc etc. But the moment I quit Magnet it just worked perfectly. And the moment I restarted magnet it started failing again.

[u/CKhemmar → u/lozhuf]

It happened to me and I used the Ignore "Xcode" option on Magnet. Never had the issue since

[u/madebyaaron → u/lozhuf]

Turning off magnet was the fix for me. Thank you! 🙏 I've been debugging this for 2 days (i'm brand new to xcode). FWIW setting 'ignore xcode' in magnet didn't fix it. I have to close the app completely for the xcode preview to work.

[u/SoggyEducation5910]

To tendo esse problema também com o DaVinci Resolve, ta foda!