Change your scaling in graphics settings, this should fix it. For me the value that caused this exact same bug was 150% scaling.
Edit: Mirrors are still bugged, but this can also be fixed by changing your mirror resolution in graphics settings. Only works with low settings for me, so if that is the case for you, try these console commands.
r_mirror_scale_y 0.9 or 1.1 (don't put it at 1)
r_mirror_scale_x 1
This should keep your mirrors at decent quality and usable