Ball jumping from water

Try to eliminate your initial hypothesis by using dimensional analysis to make a quantitative estimate based on variables you can observe and measure easily.

You should be able to estimate a Strouhal number for your system from your observations of ball diameter, 'zig-zag' frequency, and the time for the ball to reach the surface from a known depth (i.e. fluid velocity.) That should be near 0.2 for your Karman vortex hypothesis to be a viable hypothesis. If its not you may want to consider an alternative explanation.