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 "Horizontal Expansion" setting by a tiny amount seems to provide a better fix (+/- 0.001 did the job for me).
//EDIT2: The link posted above (https://service.netfabb.com/login.php) also works. I didn't expect that my CAD software messes up creating an STL from such a simple shape.