Project boards have a Menu button/link in the top right that opens a menu on the right side of the screen. That menu has an Activity scrolling list of things that have happened in the project over time, with timestamps of when they happened. In order to paginate this list of activities, there is a More button at the bottom that used to load activities starting at the end of the currently-shown activities, as one would expect. Now it simply loads the same list of activities that were already shown below the existing ones, essentially just duplicating all of the already-shown ones at the bottom of the list. It does this every time the More button is clicked, just adding more duplicates.
To reproduce this, go to a project page with enough activity to paginate the activity list, such as the v5.0.2 project on Bootstrap. Click the Menu link in the top right of the board, then scroll to the bottom of the Activity list and click the More button.
I see that this specific issue was posted a few months ago, but it seems to have been ignored, perhaps because it wasn’t in a specific category.