UE 5.7 IOS26 AR Session Crashes with Memory Free

General Issues and Bug Reporting
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Summary

Starting an AR Session with UE5.7 on IOS26 crashes with.
[UE] Fatal error: [File:./Runtime/Core/Private/HAL/MallocBinned2.cpp] [Line: 900]
FMallocBinned2 Attempt to realloc an unrecognized block 0x121cb0000 canary == 0x0 != 0xe3

Switching to ANSI allocator stops the crash and the ar session works fine.

Please select what you are reporting on:

Creative

What Type of Bug are you experiencing?

Stability

Steps to Reproduce

Build an standard AR app on MAC.
Build and deploy with XCODE 26.1
Run on IOS and start an AR session.
You’ll see an instant crash.

Expected Result

No crash, operates normally.

Observed Result

MallocBinned2 realloc crash

Platform(s)

IOS

2

Same problem here.
They don’t accept bug reports on the forums. Today I actually built the Git version to check whether this crash was fixed. And 5.7.1 has just been released today as well. The crash is still present in Git too.

I submitted a report through the form today and then stumbled upon this post :slight_smile:

We’ll have to wait. For now it looks like we’ll need to stay on ANSI or 5.6 (everything works fine there).

To be able to work with Xcode 26.1 on 5.6, go to Engine/Config/Apple/Apple_SDK.json.
There are instructions there on how to add compiler and IDE versions.
In block 1, set:
"MaxVersion": "26.1.0",

In block 9, add the following clang versions to AppleVersionToLLVMVersions:
"26.0.0-19.1.5",
"26.1.0-19.1.5"

For those who came here looking for a fix:
To work around the crash in 5.7, add these lines to your game Target.cs (or wrap them so they only apply to the iOS platform):

bOverrideBuildEnvironment = true;
StaticAllocator = StaticAllocatorType.Ansi;

Then AR will start working again without crashes in 5.7 and 5.7.1. But this is not a real fix, just a workaround.

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