I’ve noticed a small bug with the settings app in KDE where the info box that pops up when you hover over something doesn’t go away. I’ve attached a screenshot of what it looks like. It has gone away when I close the settings app.
To me this is nothing but a minor annoyance, but I thought I’d pass it on.
It might help to restart the compositor. 
qdbus org.kde.KWin /Compositor suspend && qdbus org.kde.KWin /Compositor resume
If it happens a lot, then perhaps it is best to create an alias for that in your ~/.bashrc or ~/.zshrc, depending on which one you use as your interactive shell.
alias restart-compositor='qdbus org.kde.KWin /Compositor suspend && qdbus org.kde.KWin /Compositor resume'