I'm running into this problem constantly, and it's driving me nuts.

If I minimize a window to a non-full screen size, and inadvertently drag it over the top of the screen, I see a red rectangle form over the edges of the screen, and then the minimized window can't be brought back of changed. There is no way to get to the top bar of that minimized window, to drag it downward.

In playing around, it appears that the problem starts if I drag a window's top edge either up above the limits of the screen, or drag part of the window across to the second monitor.

Of note, primary monitor is portrait, and secondary monitor is landscape.

How to I prevent this from happening?

I'm having trouble attaching an image, but will try to get a usable one up later.

It happens every time I drag a window across the monitors, whether I exit and go back in or not.

OK. Tried that. And it still happened.

So then I had a brainstorm and uninstalled the Dell Display Manager Software that came with the monitors. And, voila', the red box and issue vanished.

So displayfusion was not the cause, and all is well.

Thanks for the suggestions.