Looks like the "Subscribe to Blog" popup option has stopped working after a recent upgrade? We had a customisation in place so that people would be subscribed to a specific category rather than sitewide from the module so I removed this as I thought it could still be the issue however it still persists.
The form option also errors after submitting the details. In addition when I edited the module to switch it back to popup after testing the inline form the button now no longer appears at all? i can't see any Javacript errors in the console either.
https://www.screencast.com/t/CL0s9OqCuo
(Incidentally I noticed that the subscribe module now includes a "subscription type" option however when you make a choice such as "category" you can't them specify which category? I am misunderstanding what this is for?