Even though I set the setting for notifications to appear in the bottom right corner, it sometimes randomly pops up in the upper left corner instead.
I was running KDE Neon LTS 5.8.
More likely to occur if you have the Application Launcher open.
A possible dublicate of https://bugs.kde.org/show_bug.cgi?id=381130
*** This bug has been marked as a duplicate of bug 381130 ***