Call both HBO and Sam and ask when it gets fixed. Here I'm seeing some content with no captions. It's not an app bug but just content that has no captions. A few folk have a hard time accepting that not all content has been captioned.
I have a Samsung Smart TV (J5500) and I downloaded HBO GO a few days ago. However, Closed Captioning doesn't work at all.
The Smart TV supports 100% closed captioning because it works on Netflix and Hulu.