Shut down the XFCE4 panel
xfce4-panel --quit
Kill the XFCE4 config daemon
pkill xfconfd
Delete panel settings
rm -rf ~/.config/xfce4/panel
Clear xfconfd settings
rm -rf ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml
Restart the panel
xfce4-panel
This respawns xfconfd
One-line version of all of the above
xfce4-panel --quit ; pkill xfconfd ; rm -rf ~/.config/xfce4/panel ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml ; xfce4-panel;