Ads fails to initialize on iOS with .ipa build or when published to TestFlight/App Store

1. What happened

Also reported by several users starting in 5.5.0p3. Works when deployed/testing locally on iOS device directly from Xcode, however fails when building .ipa file and installing that.

From Game Performance service have following report for a published build on Apple TestFlight:

EntryPointNotFoundException: Unable to find an entry point named 'UnityAdsEngineSetReadyCallback' in '__InternalDynamic'.

Workaround is to use Ads SDK from asset store package: https://www.assetstore.unity3d.com/en/#!/content/66123

2. How we can reproduce it using the example you attached

1. Clone https://github.com/Unity-Technologies/unity-ads-engineintegration-test

2. Test locally by running from Xcode, verify ads are shown

3. In Xcode, select Project->Archive

4. In the Archives window, select Export -> "Save for Development Deployment"

5. Install the produced .ipa file, e.g. using iTunes

Expected: Ads are shown

Actual: Ads not shown