GetUserPerisistentVarWithNullFallback argument at position 0 was the server player

I'm trying to set a player variable, and I get this error:

Error Handling Event:
Error: Exception encountered running bridge method 'GetUserPersistentVarWithNullFallback': GetUserPersistentVarWithNullFallback argument at position 0 was the server player, which is not supported in this method
    at Object.invoke (horizon-global.js:156:23)
    at Object.getPlayerVariable (file://horizon/horizon/core/HorizonCore.js:6490:36)
    at NPCMonster.onProjectileHitMe (NPCMonster.ts:90:56)
    at NPCMonster.ts:72:11
    at file://horizon/horizon/core/HorizonCore.js:7604:24
    at Function.TracingIntegration.trace [as trace] (file://horizon/horizon/core/HorizonCore.js:7833:9)
    at file://horizon/horizon/core/HorizonCore.js:7599:32

The code  in question is a broadcast event I emit from my projectile script for the projectile shooter gizmo. When it hits an entity I send the event like this:

  private onProjectileHitEntity(entity: Entity, position: Vec3, normal: Vec3) {

    this.sendNetworkBroadcastEvent(ProjectileHitMe, { player: this.props.projectileLauncher!.owner.get(), entity: entity });
    this.onHitGeneric(position, normal);
  }

And in the broadcastevent handler for my monster I try and set a player var using that owner player parameter:

  private onProjectileHitMe(player : hz.Player, entity : hz.Entity) {

    console.log("projectile hit entity");

    if (entity == this.entity) {
      this.hit();

      let blastedZombies = this.world.persistentStorage.getPlayerVariable(player, "ChickenPlayers:BlastedZombies");
      this.world.persistentStorage.setPlayerVariable(player, "ChickenPlayers:BlastedPlayers", blastedZombies + 1);
    }
  }

This script is using default execution. So I'm not sure why it doesn't like the player I'm passing in--is the owner player on the projectile shooter gizmo not the right player object to use?