Window opens but immediately disappears. This happens with multiple apps Recently, I've run into problems with Notes, Mail, Messages, and iTerm. All of these are in my dock along with several other apps. Normally if I click on one of these it opens and works fine. Sometimes, however, one of these will open but the window will immediately disappear. I'll have to fiddle around with menu items like "Open New Viewer Window", "New Note", "New Message" or in case of iTerm I may be able to right click and see a window name I can select. Bottom line is these apps open but the window disappears. Does anyone have a clue why this happens?
If you once had them in full screen mode, by pressing the green plus sign(+) in the top-left corner, it may be reopening them into new full-screen views, which is called Mission Control. 

To check, do any of the following:


On a trackpad, swipe left or right with three or four fingers. On a Magic Mouse, swipe with two fingers.
Press the Control key and the Right or Left arrow key.
Enter Mission Control, move the pointer to the top edge of the screen to show the Spaces bar, then click a space.


Let me know if that resolves it!