A post he made awhile back is pertinent so I'll quote the relevant part.
Leaving Reddit (and twitter) was never about shutting myself out, it’s entirely because those platforms are run by vile people and I can’t stand to use them anymore. Back in the early days Reddit was 100% of my community interaction, and I admit I do miss participating in big discussion threads there, but these days the majority of my communication time is through direct messages (mainly email) and that’s been the case for years.
It seemed like it was fixed in v246 but somehow broke again in that version? I'm on v249 and still haven't seen any comments highlighted.
EDIT: I post that and then it works one time. It randomly works but mostly not for me.
EDIT2: Specifically, I have the comment button as a secondary button and when there's an orange number, that means there's new comments but when I view those posts, most of the time there's no highlighting whatsoever.