I just spent 1.5+ hrs trying to fix this after a month or so of losing productivity by sometimes having to access most notes most times only in the main window. Sometimes I could get one or more notes up in child windows but usually by the time I went to them one or twice they would disappear. I am running Windows 10 and Evernote 10.54.4 (latest).
I tried all the methods in this thread. Most did not work for me, and no single solution worked for all my windows. Matt's solution above worked for one note, and the other solution was in a MS thread which I have included below referencing Matt's. Quite possibly I will find other hidden windows that need new tricks to get them back... until Evernote gets this sorted out and saves us all a bunch of time.
Matt's worked partially (worked to get one of my missing windows back):
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To get my last window to display I used this method (https://learn.microsoft.com/en-us/answers/questions/693740/how-do-i-get-access-to-my-window-need-cascade-wind). But even then, while using this method I had to use my mouse and possibly the arrow keys at the same time... not really sure...:
Gijs Mos21Reputation points
Jan 13, 2022, 5:37 AM
Actually found a way.
hover over the app's icon on the task-bar. Thumbnails of all its windows will open.
Hover over the one that is (partially) off-screen, and right click. The windows "position" menu will open.
Select Move and use the arrow keys to get the window back on screen.
Obviously you would still need a small piece of the window already on screen to see what the arrow keys do.
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Strange though that sometimes even after doing the above methods, the same windows will disappear again, and I have to use similar methods to bring them back.