I finally upgraded my HP laptop from Lubuntu 18.04 to 18.10, but there was no familiar taskbar! I restarted for several days, until I finally searched for clues tonight.
Somehow in the upgrade, I think Openbox is managing the desktop instead of Light Panel. I right-clicked and found some menus and was able to get a terminal running. I cleared the cache and restarted, to no avail. I ran lxpanel from the terminal, and a blocky version of the taskbar I was used to came up. I also installed the Cairo dock to see what that would do.
Finally watched the intro video on the main Lubuntu site, which describes the LxQT desktop being the default. Maybe that is the issue…I’m trying to use the old desktop. Hope this helps you.
Update: Still no taskbar. Running Chrome through the right-click menu.