Hi Everyone,
We spoke to Matt about this issue and here's a summary of the discussion:
In the past these types of artifacts had multiple causes, and most of them have been fixed by now. There should no longer be horizontal line issues, and as far as we know the vertical lines only occur when using deferred shading. "Ray Trace Everything" can fix the issue, but for good results you'll need to increase the Ray Detail Modifier to 1, and this results in a slow render.
If you're using deferred shading, then we suspect the vertical lines may have something to do with adaptive sampling, therefore it might be fixable by using non-adaptive anti-aliasing (max samples). It may also be fixable by ensuring the minimum number of samples per pixel is 1. We have not tested this yet, so we're not sure.
Generally speaking, we recommend cropping the left and/or right edges in post.
Kevin