Seems to happen each time at this, the most vulnerable part of the market cycle, when market volume and rally strength is at it's weakest.
My guess is institutional trading bots are programmed to recognise sell-off conditions, kicking off specific aggressive algorithms/patterns to rattle out jittery holders, in turn helping them to walk down the price, catch a bunch of stops and accumulate for their own at best possible prices.
On the flip side, when market conditions are favourable, bots also help to walk the price upward, so it's kinda a catch 22.
