Hello Hoopera,
That is interesting. I am glad you have found that the Temporal AA is working for your project and that you have optimized your game in order to implement it.
I have a couple of questions in order to narrow down what is causing that line.
1.) What kind of lights are you using. Are they static/station/static?
2.) If they are stationary or static have you built your lighting yet?
3.) If those are metal materials, do you have a screen reflection capture inside of you scene?
4.) Have you converted your BSP brushes into static meshes?
5.) If so you will need to go to your content browser where you created the mesh. Double click on it and bring up your details panel. On the right side scroll down to the Static Mesh Settings and change the Light Map Resolution from 4 to 64 or 128.
After looking through some of these questions and troubleshoots please let me know what you find and if step five fixes the line.
Looking good for a block out so far keep it up 