My guess is that the reason the first slice is being triggered most often is because the LFO is going from -63 to +63. So when the LFO is at a negative value, it triggers slice 01 because it cannot go lower than that. I think you can fix this by setting the STRT knob to the middle value on the PLAYBACK page. I’m pretty sure this worked when I tried it, although that was several weeks ago.