LXQt global-keys takes preference over Openbox keyboard shortcuts. They include the [Super] key shortcut to open the menu, which is probably interfering with your [Super+left] key combination.
You can edit LXQt global-keys in the LXQt settings in the menu. Or you can pick combinations for your openbox shortcut keys that are “free”, like [Control+shift+arrows]
See also my earlier post: https://discourse.lubuntu.me/t/how-to-resize-windows-using-hot-keys-to-fill-50-of-the-screen/1189/2?u=thomas-n