You cannot use Fill&Sign for PDFs with digital (certificate-based) signatures because that would break the digital signature. It is possible that PDFs you want to sign have invisible digital signatures (if they are Reader-extended, for instance).
I know that.
I am not trying to do anything different from my normal practice. These are not digital signatures. When i click the "fill & sign' tab there is nothing there, no buttons, actions, nothing. It's completely empty.
Does anyone know what I'm talking about?
Adobe, I'm paying you $30 a month for something that isn't working and I can't get a consult.
Are you sure PDFs that you work with are not Reader-enabled? Can you create a simple PDF from clipboard and check if you get the same behavior?