Random Vertical Gaps between External Perimeter Geetech A30

On my Geetech A30, I've had the issues regarding print quality. Currently many of my prints having a small gap between the external layers of the perimeter. Sometimes the gap appears on just one side of the object and not the other, or all-around in different heights. I've managed to mitigate the horizontal gaps between the infill and perimeters on top, but the Vertical gaps are still plaguing my prints. For Slicing, I use Repetitor Host and Slic3r.