I need help, to solve this weird crumpling geomtry. I have displacement material, that creates streeks, but in some places it crumbles inexplicably. In material preview it loks the way I want it, but when rendered with cycles it goes wrong. What should I do?
I had a hard time to visually identify what you mean XD
I would suggest to use just the bump node in the material instead of displacement with such fine lines.
If you really want to use geomety you better make sure that your geometry has a uniform subdivision. Maybe you can add some loops cuts with ctrl+R, so no long streched triangles/squares come up in your geometry. Otherwise you will need unneccesary high subdivisions during rendering to look alright.
If you choose Experimental Featrure Set in the Render Properties tab, you can try ‘adaptive subdivison’ in the Subdivision Modifier. Be careful not to make the Dicing Scale too small
The long cube in the image demonstrates how streched triangles get subdivided