The services "runSubscriptionAutoReorders" runs every midnight by default. It checks for expired subscriptions and places a new order to extend them. It fills up a cart from the previous order and places the order.
It also sets the orderId of the old order at the cart, which is used during creation of the new order. According to this, no new order can be placed because of duplicate-entry exceptions from the database.
I will attach a patch for this.