Created attachment 162027 [details]
Screencast with slow animations to illustrate the issue

SUMMARY
When there is a notification popup in Plasma, it normally sits above the system tray. When opening a system tray applet (e.g. the volume control), the notification moves up so that it sits above the popup. This makes sense. However, the notification moves at a different speed than the popup does. This in my opinion looks awkward and gives off the feeling of one of the two lagging behind.


STEPS TO REPRODUCE
1. Create a notification (e.g. with notify-send or by downloading a file)
2. Open a system tray widget (such as volume control)


OBSERVED RESULT
Animations run at different speeds

EXPECTED RESULT
Animations run at the same speed, such that the distance between the top of the popup and the bottom of the notification is constant.
(Assuming that this distance is the same as the distance between the panel and the notification when there is no popup. I think this is the case, but haven't pixel-peeped to verify.)

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.110.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
Should probably be filed under either Notifications or System Tray, but not sure which one.

Graphics Platform: Wayland (probably not relevant)