Sickness

Try to see how the holes form. If they come with new leaves, consistent nutrient intake seems the problem, maybe PH fluctuations. If they appear later it wass by your force or by pest usually. Yours look like they appeared afterwards, cause the leaves themselves formed well and the holes arent filled with dead plant material. Looking at your new leaves though, i'd say something is a bit off withyour nutrients. They don't look as constistantly green anymore on thsi picture.

Sometimes leaves just don't grow properl;y and for no reason at all. There is nothing you can do about it and it won't affect a thing. Plants look way over fed though, especially nitrogen.