1 million share block likely placed to create a wall. Investors...

1 million share block likely placed to create a wall. Investors see sell side build with some big numbers and are reluctant to bid the SP up ... plenty of sellers, I'll keep my buy order low.
Algos can pull a sell order microseconds before it gets hit, ensuring it never gets hit.
Depending if it's genuine or not, ... if it's not then likely someone mopping up around 15.5c, 16c and not wanting the SP to run away from them.
If on the other hand the order stays and gets hit, then it's a very ordinary investor unable to wait for pending news