Blueprint base class construction not happening in packaged and standalone games

I am stumped by an issue I’m seeing I really hope someone can help sort it.

I’m using the latest version of Unreal 4.25 and have an actor in my level that behaves as expected (i.e. it animates a hand model), but this only works in simulate mode - the animation is broken in both a stand alone game and a packaged game. The hand remains static.

The actor has two skeletal mesh child components (one for each hand) and each has an animation blueprint set (Animation > Animation mode = Use Animation Blueprint + animation class set). This animation blueprint is derived from a class that I’m attempting to debug. It has an initialisation sequence that sets a variable used in the animation blueprint’s event graph that’s needed for the animation to work. When things don’t work I see that this variable is never set (I see output warnings about it being set to none). A breakpoint on the base class constructor of this animation blueprintis also not hit, suggesting the animation class is never created in standalone game or packaged game. I do see the same breakpoint hit several times when running in simulate mode. Why isn’t this animation blueprint class being created in stand alone mode? I’ve played with module dependencies and the module start up order, turning off multithreading, etc - but nothing changes.

All of this code/data comes from a plug-in in the game’s local plug-in folder.