Having troubles with d3d9wnd lately as well. When alt+tab I can't actually go out from the game to another window (chrome, discord, etc..). I see them appear but it doesn't wanna go into any. So I need to go back in the game and shift+esc (minimize). It also gives me red cursor in the middle of a screen, plenty of times, even when alt+tab works. So I need to do double alt+tab to get rid of it. Most annoying part of it all is that sometimes taskbar is shown in the game while playing and there's no way of getting rid of it, except restarting whole pc.
Don't know why. This all started maybe a week ago. Guess we need to be patient and wait for 3.8 to fix it!