The issue is that the physics components (2D colliders with 2D rigidbodies attached) are generated at runtime. They're attached to a game object called
JellySprite Reference Points which contains
JellySprite Central Ref Point and the other reference points (see screenshot)
When I apply addForce to JellySprite Central Ref Point at runtime, it all works as it should.
Any idea how I can apply force to an object that isn't in the scene until runtime?