Check out these videos for what a market maker actually is:
So, they need to reset the market making algorithm. Or shutdown the exchange for a "fix", long enough that the volatility comes back in their range.
Disabling a feature during live trading in order to ensure your company doesn't lose out on profitability, which in effect impacts market trend and activity implies manipulation. As a neutral platform whose sole purpose is to provide a place for people to buy and sell, you're essentially influencing the market by disabling/enabling buy/sells, especially at heightened times of flux.
As many have pointed it out on this thread, GDAX - the exchange works just fine. So people who are worried about selling/buying can find a willing participant on the exchange.
But, Coinbase's main site is just another willing participant just like you and me in a given trade. It can refuse to take the other side of the trade if it affects their profits.
If you still insist it is "manipulation" then I digress.
Volatility is traditionally where many styles of traders actually make money.
https://news.ycombinator.com/item?id=15988939
It seems Coinbase's go to strategy every time markets are volatile. In case people are wondering why is this a recurring problem - this simply perils of Market Making in a volatile market. As a market maker for customer orders Coinbase needs to fulfill both sides. So to make money they buy from customers at low price and sell back at a high price. So they are collecting spread between bid and ask to make money.
But what happens if the market moves rapidly in one direction? They end up selling low and buying high.
So, they need to reset the market making algorithm. Or shutdown the site for a "fix", long enough that the volatility comes back in their range.
And what was wrong with the BCH rollout?