Ah, so it is not the same as @Aranjedeath 's situation, as their screenshot clearly shows the panel in edit mode.
Another thing that you can try to do (instead of restarting plasma shell) is to run a Plasma script to set your panel location, and see if that works. If it does - it will tell us something about the situation.
To run, start the Plasma desktop scripting shell by running plasma-interactiveconsole (from the main menu, krunner, or anywhere), paste the following script in and press “Execute”:
for (let p of panels()) { p.location = 'bottom'; }
If this works, you can also run it from a script directly by running:
qdbus org.kde.plasmashell /PlasmaShell \
org.kde.PlasmaShell.evaluateScript \
"for (let p of panels()) { p.location = 'bottom'; }"