I reproduced this and I am currently working on a fix that will hopefully go into our open beta.
This issue seems to be caused by Apple’s system font which is the default for captions.
This issue also affects other languages that require fonts to have certain glyphs.
I’ll be able to fix this by falling back to an appropriate font.
I have a workaround for tvOS if this helps:
Go to Settings > Accessibility > Hearing > Subtitles and Captioning > Style > Edit Styles
Create a New Style
For “Font”, you should be able to select “Helvetica”
This seems to work around the issue for now.
Unfortunately, I have not found a workaround for iOS.
Edit: This may not work for all languages. I’m seeing inconsistent behavior as i test more.
