If you right click an asset you can choose “get reference” and it will result in this format:
WidgetBlueprint'/Game/Blueprints/UI/SomeWidget.SomeWidget'
Can you test this in these formats?:
/Game/Blueprints/UI/SomeWidget.SomeWidget'
WidgetBlueprint'/Game/Blueprints/UI/SomeWidget.SomeWidget'