@gdpelican Have you seen this?
I tried on a non-production server: removing babble results in may many, maybe hundreds of tiny user groups, mostly with two people in it, some even with 1 or 0.
And they show up as recommended topics.
Reinstalling babble makes them disappear.
However, I had a good reason to uninstall it so reinstalling is not a wtorkaround for me. (and besides this would be a strange way to go about something like this imo).