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.
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
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):
I accidentally updated to 5.6.1 from 5.6 (which was working with 16.2 xcode) do you know if there is a known issue with 5.6.1, or if it still works there as well?
I’m currently using:
UE 5.6.1, macOS 26.4.1, and Xcode 26.4 - no issues at all.
To make 5.6.1 work with the new Xcode 26 and fix the error Platform Mac is not a valid platform to build :
Open the engine path: /Engine/Config/Apple/Apple_SDK.json
You need to change the maximum Xcode version (I set it to 26.9)
In AppleVersionToLLVMVersions, add an entry for Xcode 26 specifying which LLVM version it should use.
There’s a link in that file explaining what exactly to put there.
For me it was:
26.0.0–19.1.5
26.4.0-21.1.6
Just keep in mind that in the new Xcode 26 you now need to manually install additional tools via Settings → Components.
UE requires the Metal Toolchain to match the Xcode version. It needs to be installed from the settings and updated manually
In UE 5.7, the ARKit crash can be worked around with a single line from my previous message.
I submitted several bug reports from multiple accounts, but didn’t receive any response except for an automated reply…
In the Git version of the engine, the issue is still not fixed.
