How about this possibility? Perhaps MMs realized there were a few million shares of MVNT that recently became unrestricted.
So in order to perhaps cover their open short positions MMs were able to "engineer" the dramatic sell off that occurred near the end of the day.
The entire 6 hrs prior to the close, the trading was very slow between basically 0187and 0209. Then (from a 1-minute chart), at 3:34 pm until the close, volume exploded. 3.47M shares were traded in the last 30 minutes!!!