I've had this problem since I first posted this thread and no results. Unlike what others say, in my case it's every equalizer I've tried. Support is either going to tell you disable the stock eq, reinstall or its a problem with the os which that seems to be the most logical reason since mine messed up after an update back in April. Since you're having a problem with your S4 and new update in guessing Samsung or Sprint haven't addressed the issue. I'm guessing since not that many people use an EQ it's not really major issue with them which ends up ruining our phones for us. Hopefully we get it fixed soon.