I hear people complain about their glass getting caught on the grinder bed which makes it hard to grind smoothly. Sometimes it's because the plastic grid that the glass rests on is worn and uneven. However, other times it's due to the fact that the glass being ground is heavily textured. The sharp 'points' are actually getting caught in the grid which causes the piece to jam and stop moving instead if sliding across the grinder.
If you are using glass that's heavily textured (most times this is clear glass) as shown below, try placing the glass upside down on the grinder surface. This will allow the smooth side of the glass to glide easily over the surface resulting in smoother passes!