ARK Invest, a technology and fintech firm run by Cathie Wood, made its largest investment in Coinbase (COIN) stock since Dec. 14 on Thursday, adding about $5.5 million of the shares, based on closing prices. The firm bought more than 158,000 shares for its ARK Fintech Innovation ETF (ARKF). While the firm has added smaller amounts of the stock in recent days, on Dec. 14 it about purchased a total of almost 300,000 shares at a closing-price cost of about $12 million. Those were allocated mainl...