Matt Ciaschini a vice president at Harvard Management Co left last month for personal reasons. One member of the endowment board said performance was not the reason for his departure. Jane Mendillo, the endowment’s chief executive officer who took over amid unprecedented losses during the 2008 financial crisis, said last week she will leave at the end of this year, citing personal reasons. Harvard, the world’s wealthiest school with a $32.7 billion endowment, posted a gain of 11.3 percent last fiscal year and an annual average return of 1.7 percent over five years, both the lowest in the Ivy League, according to data compiled by Charles Skorina & Co.