Investors in a specialty pharmacy services company whose value plunged several years after it went public have reached a $15.5 million settlement in a class-action lawsuit.Diplomat Pharmacy, Inc., was sued in 2019 in the Northern District of Illinois for allegedly violating federal securities laws. The complaint contended that, between February 2018 and November 2019, Diplomat concealed integration and service failures that led to customer complaints and losses, costing investors hundreds of millions of dollars.It also …