It's an old post, but I faced a similar problem and found a solution. When a wall thickness is a multiple of the nozzle size (e.g., 0.8 mm for a 0.4 nozzle), Cura seems to have problems deciding whether to print the wall in it's actual thickness or thinner, in which case some layers are missing. Adding a small amount, e.g., 0.01 mm, to the wall thickness, gets rid of the problem and won't affect the actual wall thickness.
//EDIT: My solution from above is tedious and only seemed to work for certain parts (in my case, parts that did not overlap OR were not merged). Changing the "Hor