This bug comes from https://udn.unrealengine.com/questions/585499/view.html which describes a problem where a licensee is trying to use the AssetManager to scan a primary asset type that is generated by a game or plugin-added blueprint subclass. This works correctly in the editor or a cooked game, but will fail in an editor executable run with -game or -cook. The reason why has to do with how the asset registry is initialized:
The summary is that things work fine in cooked game and normal editor modes, but in editor builds that are called with -game or a commandlet like cook, the asset registry's list of blueprint classes will be wrong. This breaks the asset manager scan as well as other code that might request the class hierachy of unloaded classes
This is difficult to verify as it comes from a UDN and none of our internal games have content that will activate it. Here are the theoretical steps that a programmer can verify:
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-94910 in the post.