Hi,
I'm also having this issue with Cura 3.5.0 and 3.5.1. This happens with walls with width of 1.2mm and 2.0mm. I made a series of cubes, ranging from 0.8mm to 2.3mm and sliced them with 3.4.1 and 3.5.1. These are the results:
I saw that, if I change the Top/Bottom Pattern to something different from Zig Zag, 3.5.1 behaves like 3.4.1.
I'm attaching my stl test file to help you to reproduce the issue.
Best Regards!
wall_test2.stl