Falkon's download manager insists on opening up with a specific location, which seems to be the top-right corner of the left-most screen. In my setup, my main monitor is on the right with the TV left to it. The TV is usually turned off, so I always have to retrieve the download manager window when it pops up.
It doesn't manually save/restore geometry, so that's most likely issue of your window manager if it moves new windows to powered off screens.
According to the kwin developers, this has to be a bug in Falkon, since the window gets initialized with a user-specified position.
But it doesn't: https://cgit.kde.org/falkon.git/tree/src/lib/downloads/downloadmanager.cpp
What's with this call? ``` QzTools::centerWidgetOnScreen(this); ```
Alright, that's it, sorry.
Git commit f80d827e59ad017252716ba142be787bf269eae7 by David Rosca. Committed on 02/01/2018 at 14:03. Pushed by drosca into branch 'master'. QzTools: Use correct screen for widget in centerWidgetOnScreen M +2 -2 src/lib/tools/qztools.cpp https://commits.kde.org/falkon/f80d827e59ad017252716ba142be787bf269eae7
*** Bug 388667 has been marked as a duplicate of this bug. ***