Closed Captions not displaying in Storyline 360

I am using the text to speech function to auto generate closed captioning. For some reason, when published the closed captions are not showing. It shows only an empty black box.

I've tried deleting the captions and re importing from a .vtt file, I've also tried deleting them and typing in manually. Nothing is giving a different result.

I've created other courses the same way and have not had this problem. Is there some captions setting that I need to adjust to get them to display?

 

Thank you

Danielle Josler