Now, this is just a guess, mind you, but I have suspected it was a case of a market maker unloading some of his accumulated shares onto me, albeit at an imperfect price--- for him, that is....with this constituting his mandatory end of day reconciliation.
This happened to me yesterday and I scrambled between different screens at Ameritrade, nearly called the brokerage. Think or swim showed an order had gone through but offered no details as to price or time of execution. The home screen showed no fill. But my order size did appear in the elapsed executions, I was pretty sure it was mine as it was a very peculiar number slightly under 50,000 shares.
I chalked it up to frantic trading common to Friday session closes but I don't really know.
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