Firstly, as this is my first post here, I'd like to congratulate the devs on the game. It's pretty good!
Anyway, when playing today, I found this bug: if you're aiming down the sights with a zoomed optic (> 1X), and your aiming gets cancelled because you have hit/touched an obstacle (e.g., a wall), the circle area that contains the optics sight remains on the screen, being over what's really there.
I'm including a couple of screenshots to exemplify that. In that case, I was using the PK-A (1.5X).