After making screen resolution updates (or transferring an SD card to another Raspberry Pi), your lxpanel configuration file might be corrupt and hence the Raspbian menu bar is missing.
Simply delete the current user lxpanel config file and restart the X server (or just reboot).
$ sudo rm -r ~/.config/lxpanel
$ sudo reboot
This will delete the current user lxpanel config file.
Restarting the X session (or rebooting) will create a new lxpanel config file and the menu bar should now be visible.