Same issues on 77CX. Previous browser version had other issues but not as bad as the new one. Hope it gets fixed soon, I hate that such an expensive TV has these kinds of issues. Where is the QA?
I found that turning off Adaptive Streaming using Javascript fixes the disappearing subtitle issue, but it means sacrificing video quality, so it's not a good solution. (play / pause still won't work).
Also there is no way to downgrade back to the original version.
I also have a C9, luckily I haven't and will not update the browser on that TV as it's been working great, better than the original CX browser version (new update ruined it completely).