I just started experiencing a problem with a model where hidden lines become visible only when I am panning around the model. When the view is stationary the model displays correctly. I am using shaded with edges display style.
Additionally, when I insert this particular part into an assembly the assembly then becomes infected with the same problem. This only started happening yesterday and I never experienced problems with this model or this particular phenomena before.
Attached are .mp4 videos of this problem.
I'm using SW2017 and just updated to SP4 this morning.
Assuming it is an issue with that particular part rather than your graphics card/driver
and assuming the file is proprietary and therefore you cannot attach it here -
and assuming the geometry is complete...
Try saving as STEP and/or Parasolid and read back in and run Import Diagnostics.
Does it pass quality check?
Also, you might try dragging the rollup bar up the feature tree and see if the issue suddenly disappears.
Ctrl Q