ios behavior different than editor and android

I'm developing a mobile music app with Unity 5.64. At one point, the user drags an "effect" element on a "music track" element to add the effect to the sound. This works fine in the editor and on my Android phone. On an iPhone the sound resets and plays from the start.

The code is the same - no #if statements.

How can this be debugged? Is there a known issue with Unity versions that may explain this?

Thanks.