I'm back ... ?
My hubzilla account is federating with diaspora again. It turns out that the diaspora and ActivityPub functionality was moved between Hubzilla versions.
Earlier, it was an "Add-on", which appears in the Settings menu (on the top left).
Now, it is an "App", which appears buried in the App menu -> Add Apps -> Available Apps. It does NOT appear in the add-ons Settings, or anywhere else in the Settings menu, even though the GNUSocial settings still appear in the old location.
Anyway, diaspora activity is now starting to show up here. Meh...