I´m exporting the high poly mesh collapsed, not with turbosmooth applied. And is perfectly flat. I´m getting this issue in all the big flat polys not only in that one.
Happened to me before, it's your highpoly surface that didn't perfectly flat. Try what Jerc suggested, add some support loops but for your highpoly mesh. You can check your highpoly by assign a high gloss material on Max (seems like you're using Max?) and switch the viewport display to Faceted, can you see the differences…
Hi guys, I have some experience baking in Painter but I never saw this weird issue on big flat polygons. Check this: Low poly mesh is ok. The same for the high poly. I checked the normal map and I found these 4 different color values. I have no idea how to fix this. I tried everything. Nothing works. I also baked this…