I found out that the cause was that the following settings in "aen.properties" had been rewritten without my permission.
system.popup.window.x
system.popup.window.y
Before the fix, X was 1968 and Y was 700.
So, I changed X to 1480 and Y to 213, and the popup is now output.
It
seems that the above settings can be changed just by dragging the popup
in Windows, so the operator probably moved the popup and changed the
settings, causing the popup to be output outside the screen.
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