Can't load objects from asset bundle when using AssetBundle.CreateFromFile

I have an uncompressed asset bundle with a main asset and multiple additional assets. If I load the asset bundle using WWW.LoadFromCacheOrDownload() everything is fine. However, I do not want to use the cache as the bundles are already on disk and rather large.

AssetBundle.CreateFromFile() does load the asset bundle. It reads the main asset and I can check to see if the assets are in the file using Contains(). However, when I try to load them Load() returns null.

I am building my asset bundles like this:

BuildPipeline.BuildAssetBundle(mainAsset, arrayOfObjects, savePath, BuildAssetBundleOptions.CollectDependencies | BuildAssetBundleOptions.CompleteAssets, BuildTarget.iPhone, BuildOptions.UncompressedAssetBundle);

Is there something I am missing either in my build process or in how AssetBundle.CreateFromFile() should be used?