Created attachment 124861 [details]
Screenshot of the issue.
As you can see in the screenshot, one notification's height was too small, resulting in an overlap with the notification beneath.
"Do not reply to this email. You can add" and "[my mail address] has 1 new" overlap.
This is the very first time I experienced it. After receiving a new notification and closing and opening the history, the issue was gone.
Operating System: Manjaro Linux
KDE Plasma Version: 5.17.4
KDE Frameworks Version: 5.66.0
Qt Version: 5.14.0
Forced Font DPI: 144
You can also see that the title of the problematic notification elides instead of line breaks as the other notification with the same content.
I also see this issue on 5.19.2
Created attachment 130348 [details]
Screenshot (Scaling: 2.0)
Still happens and also happens for scaling 2.0
Created attachment 130500 [details]
Notification Group Overlap
I just encountered this issue as well with the the same version (5.19.3).
Created attachment 139954 [details]
"show less" overlap, scale=100%
Looks like it's a duplicate and that it has been resolved. :-)
*** This bug has been marked as a duplicate of bug 427894 ***