https://issuetracker.unity3d.com/issues/android-folders-under-streamingassets-that-start-with-the-underscore-character-are-not-copied-on-android-builds
Unity Issue Tracker - [Android] Folders under StreamingAssets that start with the underscore...
A folder under StreamingAssets with a name starting with the underscore character is not copied to the final APK on Android builds.
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