Hi there and thank you for the issue.
I took a look at this and it appears to be a game bug. I can make it happen the same on native Windows.
There seems to be some alt-tab shenanigans going on as i can make the issue go away by doing a quick alt-tab out and in. Ditto it is also a way to make it happen again after that.
I appreciate you taking the time to test this Blisto! I've noticed usually the HUD elements or menu will glitch out and thats not that annoying or noticeable most of the time, but these scope overlays are bugged as hell. I think we can close this as it's not a vkd3d-proton bug.
proton 2.14x1 2024-12
The game UI elements exhibit corruption when playing in DX12.

Here's a video for you - https://youtu.be/VgEkuxkny7E?si=LUOnRZ2ZeauVLgyZ
Software information
Star Wars: Battlefront II, High settings, DX12
System information
Log files
SWBFII-VKD3DLOG.txt
SWBFII-PROTONLOG.txt