I’ve had that problem since before the redesign.
The forum also ran into serious problems with e-mail delivery immediately after the switch to Discourse, due to RPS going from direct mailing to ‘outsourcing’ to a third-party that, I believe, also ran analytics. Certain users simply couldn’t receive any e-mail from the forum, ultimately RPS gave up and reverted to direct mailing.
Since I delete mail notifications after use, with few exceptions, I’ve lost track when the mails stopped being delivered, the last notification I have kept is dated February, 4.
If no e-mails are coming through, at all, password resets are also dead.
Make sure your Email settings under Preferences are set to send e-mails every single time. In particular you need to have
[X} Send me email notifications even when I am active on the site
Additionally, I think you need to have notifications set, on at least the topic, to Watching.