I'm familiar with two things that may cause bumps- scratching the nail plate during prep, and causing bits to stick up, and the stupid little bits you get left on the nail from cotton pads when cleansing the nail.
Even using 'lint free' wipes, I still get a few fuzzies or fibres left in the nail every now and again. You have to be meticulous in getting rid of them before you polish! If I do notice bumps from a fuzzy when i've just polished, it's easy to remove, or if you've already cured the color, a gentle, quick swipe with a fine grit file will usually remove and you can repaint.
If this isn't the case, perhaps you need to look at your cuticle removal, and whether you're scratching the nail or scraping the nail plate?
Hope this helps xx