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MJ - an Iceberg order is used to show small size while hiding the majority of the order - just like an iceberg which sits mainly under water.

Your theory is incorrect as an iceberg order does not show pre-mkt and then disappear.

This is a fake order, or an order from someone seeking queue position early in anticipation of an announcement, who then cancels if no announcement made premkt.

The positive is that an algo is adding bids at lower levels when this comes in, which indicates institutional interest in this stock once momentum is shown