Hi there.

Are you only seeing the lines when you render? It looks like a tessellation issue to me.
1. Did you do a lot of mesh reconstruction in those areas at some point? Maybe go back and look at the geo to make sure it's not breaking.

2. By Chance do you have "Render Viewport Subdivision" turned on in your Render Globals? Might be causing this issue if edges aren't built correctly.

3. Are you using displacement? Maybe turn up your subdivisions.

Hard to tell without looking at your scene file, but maybe start there.

Best!