I think that more than anything else, we are seeing a...

I think that more than anything else, we are seeing a combination of two things occuring. Firstly a large index fund like Blackrock could be just unwinding via an algo program this will be done at a Volume Weighted Average Price (VWAP)throughout the day and week.
Secondly, a predatory algo system may have found the first Fund algo and then systematically will front run and profit from the trading system that it has recognised.

These predatory Algo systems scan the markets looking for the algo footprint of the big funds and then they exploit those systems. I'm sure its more of the index selling more than anything but by looking at the course of trades, it looks like more is occuring.
R