Those reasons for selling might be there.

However, if it was a real sale on the open market, and not an attempt to cap the price, most investors, including institutions, would raise the ask a little with each "tranche" if they noticed that they were selling well. Even a short-seller would likely do this.

A long, noticing a lot of selling pressure, would still back off on the offer price with each "tranche" if they were trying to maximize their eventual profit.

The obvious lack of trying to raise the price with repeated "tranches" of sales is what is the fishy part of this.

It could be a short seller trying to defend the price, but where do they get all their ammunition?

And what makes them think they will succeed in making a profit on all these short sales given the fundamentals of the company?

Meanwhile, they are just accumulating more shorts they will have to cover with the better and better news that is due to come out of PEM.

For an institution, or even a well-funded individual investor, to do this without some other motive is just plain nuts!

You need to look at what the investor stands to gain. The only scenario that is reasonably rational is if they can translate this into bigger gains elsewhere - like a PP