Straight to the point: Try /run SetCVar("rawMouseEnable", 1)
This has been happening to me since around the day this topic was started. The number of monitors has nothing to do with it, because I have a single monitor and I still get this issue.
It’s a band-aid fix, but it seems to be one solution that doesn’t require the player to completely exit the game: it appears the command /run SetCVar("rawMouseEnable", 1) will allow you to move your mouse to the borders of the screen and your camera will still move as expected rather than being stuck. I am not sure if the sensitivity is still affected or not, but it seemed to work for me. I am using the ‘Fullscreen (Windowed)’ option and haven’t seen any issues so far. I am not sure how this will work with more than one monitor, but hopefully it does help.
Just remember to use a maximized window if you intend to use Windowed mode, because the cursor will leave the boundaries of the window, or just have the ‘Lock Cursor to Window’ option enabled. The cursor will also still be the 4 way arrow, but it’s better than nothing!