It turns out it was just a nanite issue. I disabled it and now it’s fine. Not sure why it “roughened up” those meshes when they were so close to the camera.
Nanite dynamically changes the amount of drawn triangles, so if you have it enabled, it’ll override your mesh’s complexity, which can result in unreliable spline quality.
It’s been a while since I created a spline, so I was so confused why my spline was so jagged, then Clockwork reminded me to add triangles to it to smooth it out.