I'm using your smart effector. Everything was pretty square so that's why it was so confusing (using those round bubble levels on the effector and bed, etc). Found out that one of my stepper pulleys was skipping occasionally as well (grub screw not tight on the shaft somehow). Seems to be behaving pretty well. I turned off mesh bed leveling as it's not really needed, I managed to print a 350mm diameter circle with just the auto cal.
Thanks!