The flagship fund of Paul Isaac’s Arbiter Partners is on track for its worst annual performance since 2011.The $565 million vehicle, Arbiter Partners QP, was down 14.3% at the end of September, having posted losses in six of the first nine months of the year — including a 10.3% drop in June. The firm’s opportunistic-value strategy tends to be highly volatile, with four years of double-digit profits and four years of losses in...