I’m new to unreal my self, but I’ll still take a swing at this. My guess is that is has something to do with either the block all selection or some sort of displacement that occurs as a result of jumping (eg. if for walking the Actor’s distance above ground is fixed.
But, here is a note from Block in the documentation: “If the other Physics Body is set to Block this Physics Body’s Object Type, a Hit Event can occur.” Is the actor’s physics body set to block?