Was able to solve it by changing the order of the UINTERFACE specifiers.
By using UINTERFACE(NotBlueprintable, BlueprintType) instead of UINTERFACE(BlueprintType, NotBlueprintable).
So while using NotBlueprintable and BlueprintType together there order must be this way for the type cast showing up in blueprints.
Tested this for UE 5.0 and 5.1.