I use two monitors and today I noticed when I clicked on to my second monitor (to pause a video) then back to the game, the controls got stuck. The mouse cursor disappeared and was being forced to the center of the screen. Moving the mouse would turn the camera and show the cursor sometimes. I could only move using the W key to go forward. Because the focus was on the center of the screen, even if I could get the mouse pointer on to a menu item - you couldn't click it.
This has happened when alt-tabbing to a browser on the same monitor and when interacting with my second monitor. Attached is a screenshot of messages that were being spammed when this happened.