You generally should not treat this as expected normal behavior.

From your log, the build gets quite far and only fails at:

Bundling native app for iOS

So this does not look like a general Studio Pro compile issue. It looks more like an OTA + native bundle problem, which can happen when the app contains custom native pluggable widgets.

My first guess would be this:

With OTA enabled, Mendix has to create the OTA-compatible native bundle, and one of the custom native widgets is probably introducing something that is not bundling correctly for iOS. That could be:

• an unsupported native dependency
• a React Native / widget package mismatch
• a missing import or JS package
• or a widget that works in a normal package build, but not in the OTA bundling path

So I would not say “OTA itself is broken”, but I also would not ignore the fact that it only fails when OTA is on. That usually points to widget compatibility with OTA packaging.

The most important next step is to check this file from the build output:

deployment/log/native_packager_bundle_ios_log.txt

That file usually contains the real error. The main build log only shows the final wrapper exception.

A few things I would suggest checking:

First, try to isolate whether this is really caused by one custom widget.

Temporarily remove or disable the custom native pluggable widgets and build again with OTA enabled. If the package succeeds, that narrows it down quickly.

Second, verify that each custom native widget is built against the Mendix / React Native stack used by 11.6.4. Even if it behaved similarly in 10.23.0, upgrading Studio Pro alone will not fix a widget-level compatibility issue.

Third, rebuild the widget packages themselves. If these are custom widgets maintained in-house, make sure their JS dependencies are installed correctly and the widget bundle is regenerated before importing the latest package into the app.

Also, clear local generated folders before retrying, especially if this project has gone through upgrades:

• deployment
• node_modules inside custom widget projects
• any old widget dist/build output

If this resolves your issue, please mark it as accepted.

Thank you Ahmet for the suggestions.  

I dont know how to access the log file referenced on the package build output page. It builds fine locally, but I am guessing when it builds the server locally it does not build OTA.

I removed all the native pluggable widgets, references to them on pages, and the mpk files from the widgets directory, and I am stiill seeing the same error:

Hi,

This is not a random failure — what you’re seeing is a known limitation when using OTA together with custom native pluggable widgets.

From your logs, the important part is:

• Build goes through model, Java, web → all fine
• Fails at “Bundling native app for iOS”

That means the issue is purely in the native bundling stage triggered by OTA, not your Mendix logic.

What’s actually happening

When you enable OTA:

• Mendix switches to a different native packaging flow
• It builds a JavaScript bundle (OTA bundle) instead of a full native build
• This process is stricter and has limitations on:
  • Native dependencies
  • Third-party libraries
  • Custom widget structure

If your app contains custom native pluggable widgets, OTA will fail if:

• The widget uses unsupported native modules
• The widget has incorrect dependency definitions
• The widget was not rebuilt properly after upgrade

That’s why:

• OTA OFF → normal native build → works
• OTA ON → OTA bundler → fails

Is this expected?

Yes.

In real projects, OTA + custom native widgets is a known pain point.

OTA is only fully reliable when using:

• Mendix-supported native widgets
• OTA-compatible libraries

What you should check

Open this file from your build logs:

/deployment/log/native_packager_bundle_ios_log.txt

That file will show the actual root error.

Typical issues found there:

• “Module not found”
• “Cannot resolve dependency”
• “Unsupported native module”
• Metro bundler errors

What usually fixes it

1. Rebuild all custom widgets

For every custom native widget:

• Delete node_modules
• Run:
  
• npm install
  
• npm run build
• Repackage and re-import into Mendix

After upgrading from 10 → 11, this step is critical.

2. Check widget dependencies

Inside widget package.json:

• Avoid native libraries requiring linking
• Ensure correct versions of:
  • react
  • react-native

OTA is strict about dependency compatibility.

3. Verify NativeMobileResources

Make sure:

• NativeMobileResources → latest version
• All native modules are compatible with your Mendix version

4. Identify unsupported native modules

If your widget uses:

• react-native-camera
• react-native-fs
• any custom native bridge

OTA will likely fail.

In such cases, either:

• Replace with supported alternatives
• Or remove OTA

If your app depends on custom native widgets:

• Do not enable OTA
• Use standard native build pipeline

OTA is mainly suitable when:

• No custom native code
• Only supported widgets are used

This behavior is expected when using OTA together with custom native pluggable widgets. Enabling OTA switches the build process to a stricter native bundling mechanism, which often fails if custom widgets include unsupported dependencies or are not fully compatible with the OTA pipeline. The failure in your logs occurs during the iOS native bundling step, which confirms this.

To resolve the issue, you should inspect the native_packager_bundle_ios_log.txt file to identify the exact dependency or bundling error. In most cases, rebuilding all custom widgets and verifying their dependencies resolves the issue. However, if the widgets rely on unsupported native modules, OTA cannot be used reliably, and disabling OTA is the recommended approach.

If you share that iOS log file, I can point exactly which dependency is breaking the build.

Your update is very useful. If you removed all custom native pluggable widgets, removed their references from the model, and even removed the .mpk files, but the OTA package build still fails at exactly the same step, then this no longer points to your widgets as the main cause.

At this point, it looks more like an issue in the OTA iOS bundling path itself for this app, or something still present in the native bundle generation even after the widgets were removed. The important part is that the failure is still happening only at “Bundling native app for iOS”, so the model is compiling, Java is compiling, and the normal package generation is fine. The problem is specifically in the OTA/native iOS packaging step.

So no, I would not treat this as expected behavior, and based on your latest test I also would not continue focusing on the custom widgets anymore.

What I would check next is:

Make sure there are no leftover native package references in the project after removing the widgets, especially in any native-related resources that may still be exported during packaging.

Also try creating a very small test branch from the same app and disable as much native-specific functionality as possible, then build again with OTA enabled. If even that still fails, it strongly suggests a platform-side OTA packaging issue rather than an app logic issue.

Since the build output only shows the wrapper exception and you cannot access /workspace/.../native_packager_bundle_ios_log.txt from the portal, the practical next step is probably to raise a Mendix Support ticket and include:

• the full build log
• the Mendix version
• confirmation that OTA-off succeeds
• confirmation that OTA-on fails
• confirmation that the issue still happens after removing all custom native widgets

That last point is especially important, because it shows this is reproducible even in a stripped-down version of your app.

So my conclusion would be: this does not look like normal expected behavior, and with your latest test results it now looks more like an OTA iOS packaging issue than a widget compatibility issue.

If this resolves your issue, please don't forget to mark it as accepted.