One of my users just asked this question. We have a lot of high velocity topics where scrolling through thousands of posts to find replies past that first one would be very time consuming. These aren’t the “read everything” kind of topics.
It affects me as well because I’m unable to easily find people that responded to me, their moderator. I’m definitely not able to keep up with all their chat threads.
I like the idea about a flag that would let users choose to see a grouped notification or all notifications.