I have seen a few other post about this and I saw a post from last year where they said it was fixed. I've tried replying to a chapter comment and a review but still can't claim reward. My reply was 2 sentences x 10 words.
Post Reply to earn reward does not work
4 days later
I may have experienced the same problem. But in my case, it was the ""paragraph"" comment and reply that wasn't giving me any rewards. (was it paragraph or in-line comment?)
commenting at the 'end' of the chapter worked though..
i hope this fixed yours,,