The dump is too big, too steep, it smells like somebody wants to achieve something, not somebody that cash in some gains or has to get liquidity.
Not only that, it could be a long-term plan. I created
Why is Bitcoin so stable in price after a big drop? back in September:
What is causing this?
My guess is this is manipulation, and my next guess is someone is waiting for order books to be filled before placing another big sell (or buy) order which will cause the next price jump.
This stable price more or less continued until a few days ago, when the big price drop started.