Notifications are coming again even after reading them [Private Topics plugin]

Unfortunately, we haven’t had any other reports of this so it’s difficult to pinpoint what’s happening on your site. Do you have a standard install?

Is there anything in your /logs or /sidekiq page that may provide more information?

Yes. Disabling may not completely remove the problem piece. But which plugins did you recently install? We may be able to tell if one has had problems reported.