Hi,
{id} means {order_id} for the "order number format" and {order_invoice_id} for the "invoice number format".
The order_id is incremented when a new order is created.
The order_invoice_id is incremented when an order is confirmed (usually after a payment).
So if an order is created but not confirmed, the order_id will be incremented but not the order_invoice_id and thus if you use {id} for both formats you'll get a discrepency.
If you want the invoice number format setting to use the order_id, then you need to use {order_id} instead of {id}