Wow, it’s amazing!
Not sure if this is sarcasm…
Base native classes are derived directly from UUserWidget. Base class is set in blueprints with Graph > Class settings. Works fine in editor, but refuses to package (Class not found errors). Tried casting to UBlueprint and UClass with and without _C suffix.
Anyone else been here and solved this problem (was on 4.7.6, now on 4.8.2).