The subsystem collection asks each non-abstract class's CDO whether to create an instance. A subclass does not automatically replace its parent; both can exist side by side. This explains how to move the implementation into Blueprint, how to keep a C++ fallback when the child is missing, and why GetSubsystem<T>() can still find the derived instance.
The subsystem collection scans for subclasses once, when it is initialized, and sees only classes already in memory. In a packaged build, a Blueprint class that has not been loaded by then is missed entirely: its CDO is never asked whether to create an instance. The Blueprint logic never runs, and the missing class produces no error or log entry. In the editor, the Content Browser can keep the class loaded and hide the problem.
By default, staging copies files from Content/Movies outside the pak as NonUFS, which is why .mp4 files sit loose in the build directory. Turning on bSkipMovies and listing the file under UFSMovies pulls it inside, and playback through UMediaPlayer with FileMediaSource keeps working: WmfMedia on Windows reads through IFileManager, which can access files inside the pak.
How to build a base class for a ticking UObject in a UE project: the design decisions that matter, with the complete class available in StillCooking_Tools.
A Blueprint Event Dispatcher calls its bindings in registration order unless removals have reordered the list: ProcessMulticastDelegate iterates a copy from front to back. When one handler broadcasts another dispatcher, only bindings already registered with that dispatcher are included. Bindings added by later handlers do not exist yet. In this example, registration order follows from the lifecycle phases in which the Bind Event to... nodes run across different Blueprints.
Five subsystem base classes, each with a different owner. Where the engine creates and tears down each collection, how world startup relates to actor BeginPlay, and where initialization order is no longer guaranteed.
Time = 0.0 on Set Timer by Event does not mean “immediately”. It means “clear the existing timer and do not set a new one.” The node runs without an error, the returned handle is invalid, and the only warning goes to the Output Log. In a default Shipping build, that warning isn't emitted at all.
The tooltip generator cuts the function comment off at the first @param and moves everything below it onto the individual pin tooltips. It affects every BlueprintCallable node, and it changes where you have to put warnings in your own API exposed to Blueprints.
Cast<IMyInterface>(Obj) returns nullptr when an object's interface implementation exists only in Blueprint, even though ImplementsInterface() returns true for that same object. The engine skips entries marked bImplementedByK2, so casting to an interface is safe only when that interface is explicitly blocked from Blueprint implementation.