in the ConjurerLogic.java
you are using
world.syncWorldEvent(WorldEvents.SPAWNER_SPAWNS_MOB, pos, 0);
and it creating particles like this:

for (int jx = 0; jx < 20; jx++) {
double ac = (double)pos.getX() + 0.5 + (random.nextDouble() - 0.5) * 2.0;
double ad = (double)pos.getY() + 0.5 + (random.nextDouble() - 0.5) * 2.0;
double ae = (double)pos.getZ() + 0.5 + (random.nextDouble() - 0.5) * 2.0;
this.world.addParticle(ParticleTypes.SMOKE, ac, ad, ae, 0.0, 0.0, 0.0);
this.world.addParticle(ParticleTypes.FLAME, ac, ad, ae, 0.0, 0.0, 0.0);
}

although it seems like conjurer is not supposed to emit other particles than these:
ConjuringParticleEvents.CONJURER_SUMMON.spawn(world, Vec3d.of(pos), null);

And also conjurer mob summoning does not trigger "entity_place" event like default mob spawner like this:
world.emitGameEvent(entity, GameEvent.ENTITY_PLACE, blockPos);