Crashes and non-fatal errors are missing from release builds built with Xcode 26

[RenGate]

Description

Hi Firebase team.
Since updating the build environment to Xcode 26 I noticed that both crashlogs and non-fatal issues stopped to appear in Crashlytics dashboard even though affected app versions do show up in Latest Release and Release Monitoring sections which means that Firebase SDK was properly configured.
I’ve done several tests with uploading an app to TestFlight built from exactly the same source code with Xcode version being the only difference and everything worked as expected with Xcode 16.4 while 26.0.1, 26.1 and 26.2 lead to missing data.
When a test crash is performed or non-fatal error is logged in a local debug app built with Xcode 26.*, they are properly shown in Crashlytics section if dSYMs were uploaded or a warning about missing dSYMs is shown.
Are there any known issues with Xcode 26 or iOS 26 SDK that might prevent crashlogs from reaching Firebase? The only notable change in iOS 26 SDK that I can thing of is an increase of minimum TLS version to 1.2, but I suppose Firebase servers don’t rely on TLS 1.0 or 1.1 so that is not the reason why data does not reach Crashlytics dashboard.
I can prepare a stripped down version of the app that demonstrates this issue (or some other sensitive info like identifiers and API keys) and send it to Firebase engineers if they share their work email address here. I've attached some Firebase logs from debug build, but the issue is only manifesting in release builds so keep that in mind.

Environment:
Firebase 12.7.0, Swift Package Manager
iOS 26.1
macOS 15.6.1

Reproducing the issue

1. Create a TestFlight build.
2. Log non-fatal error with Crashlytics.crashlytics().record(error:) or trigger a crash.
3. Check Crashlytics dashboard.

Firebase SDK Version

12.7.0

Xcode Version

16.4, 26.0.1, 26.1, 26.2

Installation Method

Swift Package Manager

Firebase Product(s)

Crashlytics

Targeted Platforms

iOS

Relevant Log Output

[Firebase/Crashlytics] Version 12.7.0
12.7.0 - [FirebaseAnalytics][I-ACS023007] Analytics v.12.7.0 started
12.7.0 - [FirebaseAnalytics][I-ACS023008] To enable debug logging set the following application argument: -FIRAnalyticsDebugEnabled (see http://goo.gl/RfcP7r)
12.7.0 - [FirebaseAnalytics][I-ACS044003] GoogleAppMeasurementIdentitySupport dependency is not currently linked. IDFA will not be accessible.
12.7.0 - [FirebaseAnalytics][I-ACS800023] No pending snapshot to activate. SDK name: app_measurement
12.7.0 - [FirebaseAnalytics][I-ACS023308] Failed to initiate on-device conversion measurement for retrieving aggregate first-party data. Ads account not linked to Google Analytics.
12.7.0 - [FirebaseAnalytics][I-ACS023012] Analytics collection enabled

If using Swift Package Manager, the project's Package.resolved

Expand Package.resolved snippet

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If using CocoaPods, the project's Podfile.lock

Expand Podfile.lock snippet

Replace this line with the contents of your Podfile.lock!

[rizafran]

Hi @RenGate, I tried to reproduce the issue using Xcode 26, but I'm able to see the crashes in the Crashlytics dashboard. With this, I'd recommend filing a ticket through our Firebase support so the team could investigate your project, config and dSYM file. Thanks.

[RenGate]

Thank you @rizafran
I've reached out to Firebase support team as you suggested.
In the meantime I did additional investigation. I figured out a way to enable Firebase logging for release builds and noticed the following two errors:

12.7.0 - [FirebaseCrashlytics][I-CLS000000] Crashlytics could not find the symbol for the app's main function and cannot start up. This can be resolved 2 ways depending on your setup:
 1. If you have Exported Symbols File set in your Build Settings, add "__mh_execute_header" as a newline in your Exported Symbols File.
 2. If you have -exported_symbols_list in your linker flags, remove it.
12.7.0 - [FirebaseCrashlytics][I-CLS000000] Crash reporting could not be initialized

The app that I was debugging didn't have the Exported symbols file but did have a no_exported_symbols linker flag for release builds. I've added that flag several years ago after watching the WWDC 2022 video "Link fast: Improve build and launch times" that had a suggestion to add a no_exported_symbols flag for the main app binary.
Removal of that flag fixed the crash reporting, so it looks like something changed in Xcode 26 linker. It most likely now removes more symbols than it did before, if no_exported_symbols flag is set.