My guess is that BaseHealth is not the GameplayAttribute that is modified by applying GE_WeaponDamage but there is no way to be sure as I don’t see neither how the GameplyEffect is setup nor how the BaseHealth value is derived.
For good and comprehensive documentation on GAS visit GitHub - tranek/GASDocumentation: My understanding of Unreal Engine 5's GameplayAbilitySystem plugin with a simple multiplayer sample project.