I’ve just tested this with the topic at https://meta.discourse.org/t/events-plugin/69776. There are a few users who have created a lot of posts in that topic. What I am finding is that I can scroll through their posts with my browser’s scroll bar without any problem. If, instead, I try to use the topic’s timeline to scroll through the posts, the timeline will revert to pulling in all the topic’s posts. The issue seems to happen if I scroll far enough in the timeline to cause a request to be made to the database to pull in more posts.
I’ve moved this topic to our bug category.