Some players have reported issues with beginning The Iron Maidens encounter in Blackrock Foundry when soloing the raid. The problem is simply that the Iron Maidens never jump down into the arean and begins the encounter.
Luckily it's not really a bug, but it's instead just the player that have skipped some mobs. So to begin the Iron Maidens encounter, go back to the water where you jumped down and kill the mobs in the scuba suits there. Once all of these are killed, the encounter will start, and you can progress in Blackrock Foundry.