You don't give the URL of the forum , but use of the term "subscription" suggests it may, in fact, be a mail list archive.
Could it be possible that you are getting the messages direct from the source mail list and not from Nabble? It would be helpful to provide a typical From: line as that would confirm if it is Nabble that is sending you the mail.
It will help if you also describe exactly what links you click on/keystrokes you use and what responses you get to each.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.