I am having this issue here, at xenforo.com and not on my own site. I have watched the XenPorta resource thread and noticed today that the last alert from it I got months ago. But the last reply there is from thursday. Why didn't I get any alerts?
(I haven't checked yet, but I feel other resource threads are affected too. Could this be related to the Resource Manager? Bug?)
It's happened to me before quite often, and I noticed a pattern.
Embarrassingly, it even happened on one of my own resources. Somehow completely missed an alert then I noticed my Resource thread in the What's New list, and wondered what was going on. Turns out, that because I missed the alert, I also didn't get subsequent alerts. Won't make that mistake again