When calling UnloadUnusedAssets in a script where a LoadAssetAsync has occured but asset not yet used, AssetBundleRequest.asset will sometimes instantiate with error:
The referenced script on this Behaviour is missing!
The referenced script on this Behaviour (Game Object 'TestPrefab') is missing!
GameObject (named 'TestPrefab') references runtime script in scene file. Fixing!

while( true )
{
AssetBundleRequest request = m_assetBundle.LoadAssetAsync("TestPrefab", typeof(GameObject));
yield return request;
yield return Resources.UnloadUnusedAssets();
GameObject g = Instantiate<GameObject>(request.asset as GameObject);
}

Expected result:
The loading process should not fail and error messages should not appear.

Notes:
Appears to happen less on OSX and IOS