Check around the honey in the queen starter/finisher hive...does it appear torn up with little or no honey? If so, robbers got in and won the fight. They may have torn down the QC's, but the colony may have done so themselves if they lost.
Another possibility is a rogue queen cell that was well-hidden back in the comb.
Also, queens sometimes get through old excluders.
Use robber screens on each of your colonies. The starter/finisher can have a queen excluder entry "blocker" that will keep out unwanted queens, but excluder must be removed before mating occurs.
Feed all your bees in the queen yard, especially the starter/finisher. This will reduce robbing greatly. Open only one hive at a time. In robbing season, I move honey to the top of the hive, as far from the entrance as I can. I move the brood closer to the entrance, and use a robber screen.
I hope this helps.
Another possibility is a rogue queen cell that was well-hidden back in the comb.
Also, queens sometimes get through old excluders.
Use robber screens on each of your colonies. The starter/finisher can have a queen excluder entry "blocker" that will keep out unwanted queens, but excluder must be removed before mating occurs.
Feed all your bees in the queen yard, especially the starter/finisher. This will reduce robbing greatly. Open only one hive at a time. In robbing season, I move honey to the top of the hive, as far from the entrance as I can. I move the brood closer to the entrance, and use a robber screen.
I hope this helps.