Create all the polygroups first. Then use panel loops.
Do not panel loop over and over again.
When switching from one selection tool for another, such as switching from select rectangle to slice curve, verify first that zBrush accepted switch before working on the model.
For example: Select Rectangle is the default selection when loading zBrush, but you desire to use slice curve.
press control + shift and zBrush changes to the selection state to the current selection tool.
With control + shift held down you change your brush to slice curve and then release your control + shift as oppose to immediately thinking that slice curve is ready go and you start on your model.
So release control + shift and then repress control + shift again to verify that you see slice curve as the current tool and then slice your model.