Nobody can tell you anything without proper system info or other technical details like how your audio is configured, kind of audio file used, timeline settings and screenshot of the waveform and Preview panel and so on.
reviving this topic: i recently set up a home edit suite featuring Avid Media Composer and Adobe CC 2014/2015 on a late 2013 Mac Pro trashcan, which came with El Capitan preinstalled. since everything i read recommended that you NOT try to downgrade to Yosemite (or Mavericks for that matter) i soldiered on, with mostly excellent results. however, a few glitches cropped up, not unexpectedly. one that i'm trying to figure out is this issue: audio scrubbing has ceased working on this system in AE CC 2014 - for the time being i am avoiding CC2015, due to its many issues overall. anyone have an idea on getting this functionality back?