Weird graphical issues with lighting after upscaling

Your screenshot is at 720p. The game is not upscaled, it's downscaled to 720p, assuming you're rendering at 1440p.
Again, you are mixing upscaling with higher resolution rendering, they are not the same thing.
Upscaling does not introduce any issues since it's post processing after the frame is already rendered.

For solving these kind of issues when rendering at higher resolutions, you can try different values for Resolution Scale Threshold. If you want to be sure the setting fixes it, try 1024x1024 off the bat, then lower it until you find the lowest value that doesn't cause that corruption.

You can also try to turn off Anti-Aliasing, and ensure AF is set to Auto. If these don't fix it, then it's likely there is no solution at the moment.
Some visual bugs with higher resolution rendering are known, but no solutions exist.