I'm currently on a setup with 3 monitors, side by side. The middle (second) one is the primary display, with the standard panel on top. But the pop-up notifications are showing up on the top-right corner of the first (left) monitor, which doesn't have any panel on it, instead of the top-right of the middle monitor under the panel system tray were it's supposed to appear. Reproducible: Always
I also have noticed this. I have 3 monitor setup, middle is primary and got the notifications. However sometimes i change the configuration from 3->2 monitors. Middle and right monitor is on. This for some reason makes the notifications show up on the right monitor. Arch
It should show at whichever screen the plasmoid sits on. If it doesn't, then it's a bug in Plasma itself which is passing wrong screen data to the applet.
Perhaps see #356461
In my setup, my primary monitor is the laptop screen in which the panel is. My second monitor is above the laptop screen and all notifications go to the above screen. However, all other popups that open when clicking on the applet open on the primary display just above the panel as expected. The problem is only with floating notifications.
This should now be fixed. Please retest with Plasma 5.6 and report back if it's still broken. Thanks
Still seems broken in 5.6.4 on Arch Linux. My setup is just a laptop with an external monitor.