I have found the following to be helpful to fix the panel not showing:
[user@dom0 ~]$ mkdir -p ~/xfce-bak
[user@dom0 ~]$ mv ~/.config/xfce/* ~/xfce-bak
Then log out and log back in (or reboot).
If it still doesn’t start after a reboot, try the following:
[user@dom0 ~]$ mkdir -p $HOME/.config/autostart
[user@dom0 ~]$ cat <<EOF > $HOME/.config/autostart/xfce4_panel.desktop
[Desktop Entry]
Type=Application
Terminal=false
Name=Xfce4 panel
Exec=/usr/bin/xfce4-panel
EOF