@xuelainiao That is tricky, as each individual NodeBB will have separate user databases. You may want to consider adapting the session-sharing plugin so that a cookie is saved on login and read from other the NodeBBs.
@StuartH it may have to do with how often NodeBB calls the filter:footer.build hook, and since it's a SINGLE PAGE APP, it's not much, I've seen that weirdness, but I am not too sure what to do about it, the filter is pretty straight forward. what you can do to verify that's the footer code is being generated correctly, is to view-source of the page, then search for nodebb-plugin-42 comment.
If all you need to change is a template file, you can just edit the template file stored in build/public/templates in the static:app.load hook. Since templates are compiled on demand, this will work as long as ./nodebb build is run afterwards.