Exchange-traded notes are notoriously illiquid, as discussed in Henderson, Pearson, and Wang (2015). In particular, their only market makers are generally the issuers. Therefore, any move by holders to trade ETNs can have very large price impact. Since the shares were delisted and moved to the Pink Sheets, they are even less liquid since many institutional holders will not hold OTCBB or Pink Sheets shares.
What this looks like is a pump-and-dump manipulation. Furthermore, the above liquidity issues make this ripe for such a scheme. The manipulator can just keep lifting the (wide) offer and the shares will move up quickly. That is often accompanied by a large rise in volume. Then they can start shorting shares (which could explain the fall late Wednesday) as others buy the shares based on momentum. Eventually, they end up short, buying pressure abates, and prices fall. In this case, the exit is even nastier: the announced redemption at NAV will cause the price to fall more quickly -- so their short would make money even faster. Then, they could offer a few cents over NAV to close their short position.
If you look at the price and volume chart, you can see that volume increased while the stock was moving up sharply. That looks like a typical pump-and-dump price and volume chart. That amount of volume yielded large gains, but it likely was too much for Credit Suisse to keep up with hedging or creating new shares to bring the price back down toward NAV.
