I also see this under extrusion in the corner, usually on the last corner that is being filled. My printer is a somewhat modified Anycubic 4max, with the stock direct drive extruder (currently designing a new mount to fit a titan aero). I always figured it was unevenness in the bed - I will be adding a leveling sensor as part of the new mount design, so I guess I'll see if that's true.
I tend to print a lot of stuff with thin walls, and your master builds have been a godsend. I have no idea why those mods have not made it into the main version. I just downloaded and checked the latest 4.0.0 version, and its still rubbish. see the two screenshots below. this is a wall test print i made, with the wall varying in thickness from 0.2mm at the bottom up to 1mm at the top, in 0.1mm steps. The first screenshot is the latest mainline build, and the second is the master build by Smartavionics
Settings same in both cases, print thin walls enabled. I use a mac, and sadly Smartavionics has stopped making these master builds for mac. I'd be happy to build them for you if that would help get around the hardware issue... for now i'm stuck having to boot into windows every time i need to use cura, which is annoying.