I created a landscape in World Partition and applied an auto-landscape material to it (landscape, and all proxies get the same material). That worked, but now I have one proxy that does show the default material (grey checkerboard).
Whatever I try, the auto-landscape material is NOT applied to that proxy, it remains a grey checkerboard: Fill layer, paint the autolandscape material on the proxy…
Found the landscape is set to have Nanite enabled - so this proxy as well. . I don’t know why this single proxy didn’t show the landscape material, but “rebuild data” solve the issue.
