My first guess is your speeds might be too high resulting in missed steps. You could also have an unrelated issue with the glass bed moving around. Again, just a guess, keep us posted and if needed I'll post some other ideas.
On the Inside of the vase is it bulging or concave?
If it is bulging then the problem would be that too much plastic is being extruded causing it to bulge inside and out. In that case it may be cheap filament that is thick in some parts and thin in others.
If it is concave on the inside then that means the print head is not lined up when it goes back over the same area. I agree that speed can cause that problem. Loose belts or wobbly pulleys can also cause the problem.