Windows that are just invisible, as if they're located somewhere off-screen.
Windows that spawn in random places (such as the 3rd external monitor way outside my FOV), instead of following a logical rule like "on the same desktop as the cursor" or "on the desktop where this app is usually located".
Windows that get stuck in the middle of one of the fullscreen-related animations.
Oh, and that hilarious bug where the screen locker does not completely lock, so Outlook manages to show modal dialogs (that can be interacted with!) on the lock screen.
nVidia video driver crashing every time when a thunderbolt display is attached or detached since High Sierra.
Java windows flashing after screen has been locked.
Terminal windows using 100% CPU (some sort of render bug).
Bluetooth connections constantly dropping.
Windows of 0 by 0 pixels when restoring a desktop after reboot.
Video playback in every browser stopping after about 10 seconds.
