Yep, still doing it. Peak valley peak valley, alternates every other sample, even with 20mm spacing.
Rerunning that corner now: M557
Grid: X-150.0:0.0, Y-150.0:0.0, radius 150.0, spacing 10.0, 256 points
And exactly the same thing. High along rows of X, then low along a row of X, then high, etc.
Is it possible there's something mechanically causing it to be low when it's moving one way and high when it's moving the other? That's the only thing I can think of.
By the way, here's what a large square looks like (first layer) WITHOUT mesh leveling - prints pretty good, I'm just trying to get rid of the lumps. Definitely no peak/valley surface.