When I plug a second monitor on my laptop (laptop defined as primary screen), the desktop applets stay on the laptop screen but the panel change screen. Unplugging the monitor doesn't bring the panel back. (my panel is a top-screen panel). Any more info I can bring?
I mark it confirmed: https://forum.kde.org/viewtopic.php?f=289&t=132166&p=357482#p357482
Let me point out that the problem is not only occurring when plugging monitors on or off physically. Just if you switch monitors on or off in the display settings of Plasma 5 or you try only to change the default display (where the standard panel should go then) you end up loosing the panels or, respectively, having them on the wrong screen. The issue is easily to be reproduced. It may work in the first few attempts, though, and then the issues happen. I’ve seen it on Kubuntu 16.04 and on Manjaro, so it’s independent from the distribution for sure.
Olivier, would you be able to test against latest Plasma from master (Aleix merged a patch today, which requires Qt 5.6.1) in plasma-workspace which is likely to fix your problems (if not, we need to find out further issues).
After a quick chat with Olivier on IRC, we think it's a duplicate, so marking it as that. *** This bug has been marked as a duplicate of bug 356225 ***