According to quotemedia.com there were two more trades with house 100 buying a total of 32,500 shares by way of the "TSX buy-in CDS" facility.  

I think everyone has a decent understanding of short selling.  I'll try to answer toinv's question as to the motivation for going short on RVX, or any stock for that matter.  

In broad strokes there are two reasons to go short on a stock.  

1)  The short seller believes a stock to be over valued. 

A good example would be Nortel, which in the year 2000 reached almost $125 per share.  Someone (wisely) believing that Nortel was grossly overvalued could have gone short.  We'll say the short borrows 10,000 shares and sell them resulting in proceeds of $1.25 million less fees.  

Those shares though have to be returned.  Years later Nortel was trading for less than a single dollar, which means the short seller in this case could have covered off (bought back the shares that were borrowed)  and realized a profit of more than $1 million less fees. 

Of course Nortel was eventually delisted, so if the short seller waited until that happened he would not even have to cover at all, he would get to keep the entire proceeds of his short selling (again, less fees) and would never have had to buy back the shares that were borrowed because they were no longer trading.  

2)  Shaking the tree

For this scenario I'm going to use RVX as my example.  I'm also going to consult my magic 8 ball and gaze into my crystal.  After consulting my sketchy oracles I'm going to say that with a SSRA reccomending full steam ahead on BETonMACE with no modifications needed, and positive top-line data sometime late in the year that RVX will be trading at $10 before the calander turns over to 2019. 

Being very confident of this eventuality someone would want to acquire as many shares of RVX as possible, especially at current prices.  Back in April when RVX was trading in and around $2, that's a 500% return....a gain of $8.00 per share.  But to buy shares, regardless of the price, there has to be others willing to sell shares.

We know that on April 17th news came out of a prospectus filing related to a possible secondary offering brokered through B&B.   So someone borrows 1 million shares and sells them at $1.80 which results in $1.8 million in proceeds less fees.  It also results in the PPS cratering down to around $1.30 per share.

Now the short seller has that $1.8 million sitting in his margin account, but he'll also have to have an "excess" to guard against RVX moving higher.  For a penny stock like RVX (trading under $5) it would probably require about $4.5 million in total in the margin account, so about $2.7 million on top of the $1.8 million generated by the short sale.

Why is this tree shaking done? 

The short seller is hoping that the resultant drop in the PPS will cause shareholders to engage in some fear based selling, happy to take $1.30 or so for fear it could fall even more, "$1.30 is better than $0.75 or $0.50 or maybe even nothing". 

The short seller can then realize a profit on the 1 million shares sold short by buying them back cheaper, and then buy additional shares for a long position based on his confidence that the shares will be trading at $10 by the end of 2018.

As to toinv's question:  What happens if we get some "impactful news" like a positive SSRA?

This is the reason for the "excess"....the reason the short seller had to have $4.5 million in his margin account and not just the $1.8 million generated from short selling 1 million shares at $1.80

If our short selling "friend" is still short the full 1 million shares and buyers start storming in pushing the PPS higher, then the short seller could be caught in a short squeeze.  At $1.80 he'd need to have $4.5 million in his margin account to avoid his broker buying the shares back. 

If the PPS climbed to $3 he would need to have about $7.5 million in the account.  $3 x 1,000,000 = $3,000,000 + 250% excess maintainence in case the PPS keeps climbing.  If the short seller is unwilling or unable to fund the margin account to these levels a forced buy-in would result.

Delivery Failures

Something that is important to realize is that none of us is holding our shares in certificate form, at least I highly doubt anyone has an actual cert # for their shares.  Instead we hold our shares "In Street Name". 

The actual share certs are managed through the CDS, or Canadian Depository for Securities.  In the US its called the DTC or Depository Trust Company.  Think of it as a warehouse where shares are stored.  But of course in today's digital world its actually more a repository of information, more like blockchain than an actual physcial warehouse..  

Most of us will know that trades are not "settled" right away, it takes 3 days...and now in some cases only 2.  This is called the "settlement period".  So when I sell say 10,000 shares of RVX the money doesn't show up until 2 or 3 trading days later.  This activity is managed by the CDS or DTC. 

Say someone bought 32,500 shares of RVX on Tuesday, but on Friday the shares still had not been delivered to the CDS for settlement.  This is called a delivery failure.  The person who sold them, they sold short but failed to locate the 32,500 shares they sold.  In the buyers account the 32,500 show up, but behind the scenes there is no certificate number attached to them....they don't exist. 

That is why we are seeing these TSX Buy-Ins CDS.  To settle these delivery failures the shares are bought at a 10% premium to the then market price to settle the failed delivery of shares.   

Wrapping it up

I invite anyone to verify anything and everything I've shared here.  The $10 PPS is a spit ball number based on a hypothetical situation of a +SSRA and +Top Line Data, but it is not a prediction nor obviously a sure thing.  

The delivery failures that we're now seeing pretty much every day, the last five days in a row, for me this is evidence that RVX is incredibly tightly held.  Sellers are having to go short to satisfy some of the buying, and are doing it to such a degree that some of the shares are not being delivered to the buyers. 229,500 delivery failures resulting in these forced buy ins in the last month alone.