On advice from @phenomlab I uninstalled the plugin, rebuilt, installed plugin again, rebuilt and it was ok.
This had also happened to himself before.
I'm fairly new to NodeBB so forgive me for any gaps in basic knowledge.
I have the leaderboard plugin but want to display it underneath the category list on my homepage, rather than a whole different route. Sounds like I need to make it into a widget and then add that widget to a region of the page.
I had a bash at converting the plugin to a widget based on the published instructions for writing a widget, and by comparing with other widgets, but currently my widget doesn't even appear in the available widgets list.
Can anyone give me an idea of how to achieve what I'm trying to do?
Do you have a repo or code to show?