No Captions or button appearing

Make sure you have the "captions" toggled on in your player settings:

I don't believe that hiding the CG-voices in the timeline affects the CCs, but it's possible that it does. 

make sure the audio files have caption, the icon will not appear on any slides that do not have caption

Thank you, yes captions are on on the player settings. I know I got this to work in the past and yes I did tick teh generate captions box when adding the text for the voice over, so still stumped

if they are hidden does that mean your human audio has no captions, hidden audio will not publish or show the caption button

As PhilMayor said, captions attached to hidden audio won't show.

If the caption are attached to the computer-generated voice, you could export them, and then import them into the human-voice audio. Edit the captions as necessary to ensure they are properly synced. 

Storyline 360: Creating and Editing Closed Captions With the Built-in Editor | Articulate - Community 

That's unfortunate. A lot of work switching things back on, exporting etc. Thanks for the replies. If only the computer generated voices sounded better and we had more UK ones!

why not export the captions and import them to your new audio?

Try this:

Set the CG-audio to "mute" and see whether that gives you the result you want.