Am I dumb or is the damage ground based arc trial bugged?

Just had my second run on blue gate trying to bang out 3-4 of these trials on one hit. During harvester so I had tunnels and warehouse to myself. Solo the bombadier, started with a heavy fuse on it which is an instant 3 star, moved into tunnel and solo the bastion. While waiting for it to respawn (which it never did) I must have killed 4 shredders, 5 comets, countless pops and fireballs and obviously a heap of flying arc which I know doesn’t count. Also put about 20 long distance hullcrackers on the queen. I finished with 0 stars for ground based arc and a total of 84 points. Anyone care to educate me?