From time to time when watching various currencies or commodities I notice that out of thin air large orders appear that don't show up on the Bids and Asks. I am not referring to Iceberg orders. Those are easy to see. For example, say I notice 5 orders of 10 lots each at the offers. The Asks will usually keep reloading so it makes sense its an iceberg order such as For example it might be as such 11 1 13 3 15 5 18 8 22 11 ^ As the offer is filled, it reloaded instantely showing an iceberg order. This might happen in a split second or over the span of a few minutes. HOWEVER From time to time, I see on the offer (or bid) very little liquidity such as 5 4 9 2 4 1 3 Then all of a sudden at that EXACT price there was a huge 100 lot order that just filled. It obviously wasn't a marker order or it would have spanned a few difficult price ticks. Now I am wondering where this order came from. If some bot put a quick offer of 100 lots at the ask, and then another bot quickly took it out, it should of at least appeared on the Asks. Why is there no transparency with these orders?
Could also be an off market block trade or a trade resulting from execution on a calendar spread maybe relating to the implied book. Assuming this is cme.
Could be as a resulted of failed execution. I have had similar issues where the platform won't let me place an order. I later found out that those orders were executed afterward. So, it could be technical error.