You can get called any day without warning on a short. as you put it, that is how it is done.
Commissions are tiny compared to when I did it years ago, but the problem remains that when you reshort after getting forced to close your position there is a day or so before you can short again, and the market may have moved a lot in that time. 4 months is a long time to play that uncertain pricing game. If you want a more likely (and just as irrelevant for us investors) theory, those who participated are people like me who are accredited (Venture term for those permitted to participate) investors who held the paper previously so are selling it now. That is how I bought into the previous placement.
This topic is boring since it has no effect on anyone looking at NXT as an investment, so that is it for me. It seems most of the people here are more intent in writing a novel the topic being who shorted and who bought because of a newsletter etc, than on reality ideas that affect their investment. It will be weeks before this pp closes and no news until then.