Maybe ask them to check https://www.foodtalkcentral.com/my/notifications/responses? are the notifications they were expecting to get listed there?
Safe to assume that your account and others aren’t having the problem? If they right click and visit the inspector in their browser, do they see any errors on the console tab?
It also appears that you haven’t updated Discourse in 6+ months, so getting up-to-date could eliminate some old bugs.