I found a video on procedural Terrain generation(PROCEDURAL TERRAIN in Unity! – Mesh Generation).
I wrote the code and rechecked it. The result is this, when generating a mesh of sizes up to 200200, everything is fine, but when I specify a size of more than 300, problems with generation begin. The size is 300300. Starting from z = 217 and x = 217, the drawing of squares breaks down. I attach screenshots of the joint, the general view (green is the border of the vertices), and the view from below. I repeat, with smaller sizes, everything is well generated. It feels like the direction of the vector is breaking, although it doesn’t look like it either. What could it be? The code is purely like in the video.enter image description hereenter image description hereenter image description here

Gizmos shows that the vertices are built correctly. I tried to start rendering immediately from 200 on the z axis. Which led to the same result.