@Mike, I noticed this last night. After opening this site, I clicked on Activity, and it looked to load everything since the last time I visited. I clicked on Load More Activity. In the past, it would list more posts. Now, it doesn't do anything. I checked the site later in the evening and clicked on Activity. Nothing was listed, and again, Load More Activity did nothing. 

Has some setting changed?

I have noticed that as well. It's been like this for a while.

All it means is no new activity since you last logged in or viewed the forum. If I want to look back, them I go to Activity ---> My activity streams and select View last 24 hours.

There's a new "Last 30 Days" choice. And Week.  They're also Topic selective, not all posts.

I never had to use those before.