As the title says, 3.2.18 came with the 3.2.0 version of the Octoprint plugin.
When I tried to use this version, Cura could 'see' the temperatures reported by Octoprint (the graphs in Monitor updated) but wouldn't send print jobs. Some Googling showed this was an upstream issue in 3.2 and one needs to use version 3.2.2 of the plugin.
Trying to update the plugin as a normal (non-root) user from within cura failed (somewhat unhelpful 'install failed' error message).
I ended up deleting /usr/share/cura-lulzbot/plugins/plugins/OctoPrintPlugin (created by the .deb) and then installed the plugin from within cura (which put it in ~/.local/share/cura-lulzbot/3.2/plugins/OctoPrintPlugin). Maybe I could have just installed the plugin rather than try an update.
Restarted Cura and it's now printing via Octoprint.