Thanks. I tried same rec. region and separate, tried lowering the lower plane, closing project, new project, and restarting PC, nada. But then lowering the pixel density, that finally worked! Why? thing is, I need full resolution, the whole point of the exercise being hairline crack detection.
Not to forget, the same size region for the ortho looking up into the underbelly was able to render at full resolution. The model has 232 8K tiles, which is a lot, but my PC didn’t sweat it, don’t believe it’s system resources. I just tried rendering the missing upper half, and that worked. Interesting, but how to make sense of whatever wall I hit. Again, I have 196 GB RAM, 24 GB video RAM, not seeing the pressure, is this a bug?