Here is a post from Corundum from another board that explains how today's volume went from 3.9 million shares right before close to over 23 million shares a few minutes after close:
So I believe I have the numbers figured out. 3.9 million shares traded before the close. This may have included some that the MM needed to complete the XBI rebalance. Most of the rebalance was already allocated to other parties, possibly including other family funds. Between 16:00 and 16:00:58 the initial MOC came in at 10.4 million shares, leading the 16:00:58 shares traded figure to be at 14.3 million (see above posts with Level 2 data). The 10.4 million shares for MOC included 8 million (7,977,249) sold/transferred to other funds/investors as pre-planned. In addition, 749,055 for a LABU rebalance got recorded at 16:00:58 (Humanigen shares sold -- but not all of the LABU amount). The remaining 1.65 million shares were true MOC, which is consistent with the heavy transactions occurring in the last 30 minutes of the day, and consistent with quad witching, etc. In the next 2.5 minutes, Nasdaq recorded an additional 9.3 million in transactions, almost all of which was double booking. There is the XBI offset (7,977,249) the LABU offset (899,055 total shares), the LABU sales missed in first MOC (150,000), one transaction of 225,222 that might have been related to the XBI rebalance (if so, the true MOC excluding rebalance might have been 225,222 higher than 1.65 million)and a few small after hours sales (17,000) that might have been caught up in a restatement of MOC. So you had 3.9 million shares prior to close, 8 million XBI rebalance (offset by exact count of 7,977,249 = 8 million reported 2 minutes after close), 900,000 LABU rebalance (duplicated by another 900,000 in three transactions), 1.65 million true MOC, 225,000 transaction not sure. Equals 23.575 million total reported with the price not really moving much because it is a rebalance. There may have been rounding effects in the 3.9 million and 14.3 million figures above that lead my numbers to be slightly more than 23.5 million. Best guess overall.
