How to fix: Focus being lost for no reason (on Windows)

There is no generic solution for focus stealing, but you can use WinFocusMon Show archive.org snapshot to find out which program is stealing focus from your application. \
Note these things:

• You may need to start WinFocusMon with administrative privileges. Otherwise, it may not be able to create its log file (which you need).
• It also works with full-screen applications (like games). If you have trouble assigning the window via the "Get" button, just type the application window's name into the 1st input field yourself.
• You may want a faster polling rate. 30ms should be enough and work around accidentally focusing a window by clicking the mouse (while that window did not steal it in the first place).
• Once you've set it up, manually test that it works by switching to your application and alt-tabbing back out.