Can confirm alerts are being spotty right now. Didn't get notified about new posts in watched threads (like the stonetoss thread I watched yesterday). I just started receiving the alerts now, after catching up with the threads.
To be fair, it often happens I never find out a thread I participated in has a new post until months later because the alerts are broken until I manually go to that thread, then they start working again for a brief while, and stop working after a week or so. Maybe this is why people are relying on rating/sticker alerts, those were usually more reliable than new posts alerts in watched threads.
This is partially mended by having the Watched threads section on the homepage now, at least.