 Shares of Purple Innovation Inc. PRPL, -22.08 plummeted 21.6 toward a 17-month low in midday trading Wednesday, after a host of rating downgrades in the wake of the mattress makers delayed and disappointing third-quarter results and lowered outlook. No less than four of the 10 analysts surveyed by FactSet cut their ratings to the equivalent of hold, and six analysts cut their price targets. 