Ive had this issue for a while too, ill try and show you some images to maybe explain it in a better way.
Picture 1 - Here everything is as it should be, Notepad++ is within the area of the screen that the taskbar doesnt use, no problems here.
Picture 2 - Then i open a game thats running in fullscreen mode on the main monitor, only happens with fullscreen apps. And still everything looks fine.
Picture 3 - Then i close the game and suddenly you can see the the bottom bar of notepad++ has gone down under the taskbar area, this is the problem we are talking about.
Picture 4 - Same as before, but just showing that some apps, will go above the taskbar when this problem is active, hiding it from view.
The only way to then fix this problem is to unlock the taskbar, move it to the side and then back down to where you want it, but this only works untill you launch another app that goes fullscreen like the game does, then the problem comes back.
